U.S. patent number 7,847,438 [Application Number 12/167,812] was granted by the patent office on 2010-12-07 for power transmission device, electronic instrument, and waveform monitoring circuit.
This patent grant is currently assigned to Seiko Epson Corporation. Invention is credited to Ken Iisaka, Mikimoto Jin, Takahiro Kamijo, Kota Onishi, Haruhiko Sogabe, Kentaro Yoda.
United States Patent |
7,847,438 |
Jin , et al. |
December 7, 2010 |
Power transmission device, electronic instrument, and waveform
monitoring circuit
Abstract
A power transmission device of a non-contact power transmission
system includes a waveform monitoring circuit that generates and
outputs a waveform-monitoring induced voltage signal based on a
coil end signal of a primary coil, and a power transmission control
device that controls a power transmission driver that drives the
primary coil, the power transmission control device receiving the
waveform-monitoring induced voltage signal and detecting a change
in waveform of the induced voltage signal to detect a
power-reception-side load state. The waveform monitoring circuit
includes a first rectifier circuit having a limiter function, the
first rectifier circuit including a current-limiting resistor
provided between a coil end node where the coil end signal of the
primary coil is generated and a monitoring node where the
waveform-monitoring induced voltage signal is generated, performing
a limiter operation that clamps the induced voltage signal at a
high-potential-side power supply voltage, and subjecting the
induced voltage signal to half-wave rectification.
Inventors: |
Jin; Mikimoto (Chino,
JP), Kamijo; Takahiro (Fujimi-cho, JP),
Yoda; Kentaro (Chino, JP), Sogabe; Haruhiko
(Chino, JP), Onishi; Kota (Nagoya, JP),
Iisaka; Ken (Chino, JP) |
Assignee: |
Seiko Epson Corporation (Tokyo,
JP)
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Family
ID: |
40220863 |
Appl.
No.: |
12/167,812 |
Filed: |
July 3, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090009006 A1 |
Jan 8, 2009 |
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Foreign Application Priority Data
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Jul 4, 2007 [JP] |
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2007-175874 |
Apr 28, 2008 [JP] |
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2008-117439 |
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Current U.S.
Class: |
307/104 |
Current CPC
Class: |
H02J
50/80 (20160201); H02J 7/045 (20130101); H02J
7/025 (20130101); H02J 50/60 (20160201); H02J
7/00 (20130101); H02J 50/12 (20160201); H02J
7/04 (20130101); H02J 50/90 (20160201); H02J
7/0034 (20130101) |
Current International
Class: |
H02J
17/00 (20060101) |
Field of
Search: |
;307/104 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A-7-31064 |
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Jan 1995 |
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JP |
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A-10-260209 |
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Sep 1998 |
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JP |
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A-11-341711 |
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Dec 1999 |
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JP |
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A-2001-7745 |
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Jan 2001 |
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JP |
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A-2001-352699 |
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Dec 2001 |
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JP |
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A-2002-142356 |
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May 2002 |
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JP |
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A-2002-221567 |
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Aug 2002 |
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JP |
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A-2004-166449 |
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Jun 2004 |
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JP |
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A-2005-110421 |
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Apr 2005 |
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JP |
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A-2005-137040 |
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May 2005 |
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JP |
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A-2006-60909 |
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Mar 2006 |
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JP |
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WO 2007/010869 |
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Jan 2007 |
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WO |
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Other References
US. Appl. No. 12/163,266, filed Jun. 27, 2008 in the name of Iisaka
et al. cited by other .
U.S. Appl. No. 12/163,300, filed Jun. 27, 2008 in the name of
Iisaka et al. cited by other.
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Primary Examiner: Fureman; Jared
Assistant Examiner: Amrany; Adi
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A power transmission device included in a non-contact power
transmission system that transmits power to a power reception
device by electromagnetically coupling a primary coil and a
secondary coil to transmit power to a load of the power reception
device, the power transmission device comprising: a waveform
monitoring circuit that includes a first rectifier circuit and
generates and outputs a waveform-monitoring induced voltage signal
based on a coil end signal of the primary coil; and a power
transmission control device that controls a power transmission
driver that drives the primary coil, the power transmission control
device receiving the waveform-monitoring induced voltage signal and
detecting a waveform of the induced voltage signal to detect a
power-reception-side load state, the first rectifier circuit
including: a first resistor that is a current-limiting resistor
provided between a coil end node where the coil end signal of the
primary coil is generated and a first monitoring node where a first
induced voltage signal that is the waveform-monitoring induced
voltage signal is generated; a first diode provided between the
first monitoring node and a high-potential-side power supply node,
a forward direction of the first diode being a direction from the
first monitoring node to the high-potential-side power supply node;
and a second diode provided between the first monitoring node and a
low-potential-side power supply node, a forward direction of the
second diode being a direction from the low-potential-side power
supply node to the first monitoring node.
2. The power transmission device as defined in claim 1, the power
transmission control device including a waveform detection circuit
that detects a change in waveform of the induced voltage signal of
the primary coil; the waveform detection circuit including: a first
waveform detection circuit that detects a waveform of the first
induced voltage signal of the primary coil; and a second waveform
detection circuit that detects a waveform of a second induced
voltage signal of the primary coil; and the waveform monitoring
circuit including: the first rectifier circuit that outputs the
waveform-monitoring first induced voltage signal to the first
waveform detection circuit through the first monitoring node; and a
second rectifier circuit that outputs the waveform-monitoring
second induced voltage signal to the second waveform detection
circuit through a second monitoring node.
3. The power transmission device as defined in claim 2, the second
rectifier circuit including: a second resistor provided between the
coil end node and the second monitoring node; a third resistor
provided between the second monitoring node and a
low-potential-side power supply node; and a third diode provided
between the second monitoring node and the low-potential-side power
supply node, a forward direction of the third diode being a
direction from the low-potential-side power supply node to the
second monitoring node.
4. The power transmission device as defined in claim 2, the power
transmission control device including: a drive clock signal
generation circuit that generates and outputs a drive clock signal
that specifies a drive frequency of the primary coil; a driver
control circuit that generates a driver control signal based on the
drive clock signal, and outputs the driver control signal to the
power transmission driver that drives the primary coil; and a
control circuit that detects the power-reception-side load state
based on a detection result of the waveform detection circuit; the
first waveform detection circuit of the waveform detection circuit
including a first pulse width detection circuit, when a timing at
which the first induced voltage signal that has changed from a
low-potential-side power supply voltage exceeds a first threshold
voltage is referred to as a first timing, the first pulse width
detection circuit measuring a first pulse width period to detect
first pulse width information, the first pulse width period being a
period between a first edge timing of the drive clock signal and
the first timing; and the control circuit detecting the
power-reception-side load state based on the first pulse width
information.
5. The power transmission device as defined in claim 4, the first
waveform detection circuit including a first waveform adjusting
circuit that adjusts a waveform of the first induced voltage signal
and outputs a first waveform-adjusted signal; and the first pulse
width detection circuit measuring the first pulse width period
based on the first waveform-adjusted signal and the drive clock
signal.
6. The power transmission device as defined in claim 5, the first
pulse width detection circuit including a first counter that
increments or decrements a count value in the first pulse width
period and measures the first pulse width period based on resulting
count value of the first counter.
7. The power transmission device as defined in claim 4, the control
circuit performing primary foreign object detection based on the
first pulse width information, the primary foreign object detection
being foreign object detection before normal power transmission
starts.
8. The power transmission device as defined in claim 7, the second
waveform detection circuit including a second pulse width detection
circuit that measures a second pulse width period and detects
second pulse width information, the second pulse width period being
a period between a second edge timing of the drive clock signal and
a second timing, the second timing being a timing when the second
induced voltage signal of the primary coil that has changed from a
high-potential-side power supply voltage falls below a second
threshold voltage; and the control circuit performing secondary
foreign object detection based on the second pulse width
information, the secondary foreign object detection being foreign
object detection after normal power transmission has started.
9. The power transmission device as defined in claim 8, the second
waveform detection circuit including a second waveform adjusting
circuit that adjusts a waveform of the second induced voltage
signal and outputs a second waveform-adjusted signal; and the
second pulse width detection circuit measuring the second pulse
width period based on the second waveform-adjusted signal and the
drive clock signal.
10. The power transmission device as defined in claim 9, the second
pulse width detection circuit including a second counter that
increments or decrements a count value in the second pulse width
period and measures the second pulse width period based on
resulting count value of the second counter.
11. The power transmission control device as defined in claim 9,
the first waveform detection circuit including a first waveform
adjusting circuit that adjusts a waveform of the first induced
voltage signal and outputs a first waveform-adjusted signal to the
first pulse width detection circuit; and the second waveform
adjusting circuit adjusting a waveform of the second induced
voltage signal differing from the first induced voltage signal, and
outputting the second waveform-adjusted signal to the second pulse
width detection circuit.
12. The power transmission device as defined in claim 1, the power
transmission control device including a waveform detection circuit
that detects a change in waveform of the induced voltage signal of
the primary coil; the waveform detection circuit including: a first
waveform detection circuit that detects a waveform of the first
induced voltage signal of the primary coil; and a second waveform
detection circuit that detects a waveform of a second induced
voltage signal of the primary coil; the waveform monitoring circuit
including: the first rectifier circuit that outputs the
waveform-monitoring first induced voltage signal to the first
waveform detection circuit through the first monitoring node; and a
second rectifier circuit that outputs the waveform-monitoring
second induced voltage signal to the second waveform detection
circuit through a second monitoring node; the second rectifier
circuit including: a third diode provided between the second
monitoring node and the high-potential-side power supply node, a
forward direction of the third diode being a direction from the
second monitoring node to the high-potential-side power supply
node; a fourth diode provided between the second monitoring node
and the low-potential-side power supply node, a forward direction
of the fourth diode being a direction from the low-potential-side
power supply node to the second monitoring node; a second resistor
provided between the third diode and the second monitoring node; a
third resistor provided between the second monitoring node and the
low-potential-side power supply node; and a second capacitor
provided between a high-potential-side resistor end node and the
coil end node, the high-potential-side resistor end node being
provided between the third diode and the second resistor.
13. The power transmission device as defined in claim 12, the power
transmission control device including: a drive clock signal
generation circuit that generates and outputs a drive clock signal
that specifies a drive frequency of the primary coil; a driver
control circuit that generates a driver control signal based on the
drive clock signal, and outputs the driver control signal to the
power transmission driver that drives the primary coil; and a
control circuit that detects the power-reception-side load state
based on a detection result of the waveform detection circuit; and
the first waveform detection circuit of the waveform detection
circuit including a first pulse width detection circuit, when a
timing at which the first induced voltage signal that has changed
from a low-potential-side power supply voltage exceeds a first
threshold voltage is referred to as a first timing, the first pulse
width detection circuit measuring a first pulse width period to
detect first pulse width information, the first pulse width period
being a period between a first edge timing of the drive clock
signal and the first timing.
14. The power transmission device as defined in claim 13, the
second waveform detection circuit including a second pulse width
detection circuit that measures a second pulse width period and
detects second pulse width information, the second pulse width
period being a period between a second edge timing of the drive
clock signal and a second timing, the second timing being a timing
when the second induced voltage signal of the primary coil that has
changed from a high-potential-side power supply voltage falls below
a second threshold voltage.
15. An electronic instrument comprising the power transmission
device as defined in claim 1.
16. A power transmission device included in a non-contact power
transmission system that transmits power to a power reception
device by electromagnetically coupling a primary coil and a
secondary coil to transmit power to a load of the power reception
device, the power transmission device comprising: a waveform
monitoring circuit that includes a first rectifier circuit and
generates and outputs a waveform-monitoring induced voltage signal
based on a coil end signal of the primary coil; and a power
transmission control device that controls a power transmission
driver that drives the primary coil, the power transmission control
device receiving the waveform-monitoring induced voltage signal and
detecting a waveform of the induced voltage signal to detect a
power-reception-side load state, the first rectifier circuit
including: a first resistor that is a current-limiting resistor
provided between a coil end node where the coil end signal of the
primary coil is generated and a first monitoring node where a first
induced voltage signal that is the waveform-monitoring induced
voltage signal is generated; and a Zener diode provided between the
first monitoring node and a low-potential-side power supply node, a
forward direction of the Zener diode being a direction from the
low-potential-side power supply node to the first monitoring
node.
17. A power transmission device included in a non-contact power
transmission system that transmits power to a power reception
device by electromagnetically coupling a primary coil and a
secondary coil to transmit power to a load of the power reception
device, the power transmission device comprising: a waveform
monitoring circuit that includes a first rectifier circuit and
generates and outputs a waveform-monitoring induced voltage signal
based on a coil end signal of the primary coil; and a power
transmission control device that controls a power transmission
driver that drives the primary coil, the power transmission control
device receiving the waveform-monitoring induced voltage signal and
detecting a waveform of the induced voltage signal to detect a
power-reception-side load state, the first rectifier circuit
including: a first capacitor provided between a first node and a
coil end node where the coil end signal of the primary coil is
generated; a first resistor that is a current-limiting resistor
provided between the first node and a first monitoring node where a
first induced voltage signal that is the waveform-monitoring
induced voltage signal is generated; a first diode provided between
the first monitoring node and a high-potential-side power supply
node, a forward direction of the first diode being a direction from
the first monitoring node to the high-potential-side power supply
node; and a second diode provided between the first node and a
low-potential-side power supply node, a forward direction of the
second diode being a direction from the low-potential-side power
supply node to the first node.
Description
This application claims priority from Japanese Patent Application
No. 2007-175874, filed in the Japanese Patent Office on Jul. 4,
2007 and Japanese Patent Application No. 2008-117439, filed in the
Japanese Patent Office on Apr. 28, 2008, the entire discloses of
which are hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
The present invention relates to a power transmission device, an
electronic instrument, a waveform monitoring circuit, and the
like.
In recent years, non-contact power transmission (contactless power
transmission) that utilizes electromagnetic induction to enable
power transmission without metal-to-metal contact has attracted
attention. As application examples of non-contact power
transmission, charging a portable telephone, charging a household
appliance (e.g., telephone handset), and the like have been
proposed.
As related-art non-contact power transmission technology, a power
transmission device has been known which implements data
transmission from a power reception device (secondary side) to a
power transmission device (primary side) by means of load
modulation (e.g., JP-A-2006-60909). The power transmission device
detects a change in power-reception-side (secondary-side) load
state due to foreign object insertion or data transmission by
detecting the induced voltage in a primary coil using a comparator
or the like.
The above-mentioned power transmission device generates an induced
voltage signal input to a power transmission control device by
means of voltage division using a resistor. Therefore, the waveform
is reduced due to voltage division, whereby the load state
detection accuracy cannot be improved to a satisfactory level.
SUMMARY
According to one aspect of the invention, there is provided a power
transmission device included in a non-contact power transmission
system that transmits power to a power reception device by
electromagnetically coupling a primary coil and a secondary coil to
transmit power to a load of the power reception device, the power
transmission device comprising:
a waveform monitoring circuit that generates and outputs a
waveform-monitoring induced voltage signal based on a coil end
signal of the primary coil; and
a power transmission control device that controls a power
transmission driver that drives the primary coil, the power
transmission control device receiving the waveform-monitoring
induced voltage signal and detecting a waveform of the induced
voltage signal to detect a power-reception-side load state,
the waveform monitoring circuit including a first rectifier circuit
having a limiter function, the first rectifier circuit including a
first resistor that is a current-limiting resistor provided between
a coil end node where the coil end signal of the primary coil is
generated and a first monitoring node where a waveform-monitoring
first induced voltage signal is generated, performing a limiter
operation that clamps the first induced voltage signal at a
high-potential-side power supply voltage, and performing a
half-wave rectification of the first induced voltage signal.
According to another aspect of the invention, there is provided an
electronic instrument comprising the above power transmission
device.
According to another aspect of the invention, there is provided a
waveform monitoring circuit provided in a power transmission device
included in a non-contact power transmission system that transmits
power to a power reception device by electromagnetically coupling a
primary coil and a secondary coil to transmit power to a load of
the power reception device, the waveform monitoring circuit
comprising:
a first rectifier circuit having a limiter function, the first
rectifier circuit including a first resistor that is a
current-limiting resistor provided between a coil end node where a
coil end signal of the primary coil is generated and a first
monitoring node where a waveform-monitoring first induced voltage
signal is generated, performing a limiter operation that clamps the
first induced voltage signal at a high-potential-side power supply
voltage, performing a half-wave rectification of the first induced
voltage signal, and outputting the first induced voltage signal to
a power transmission control device of the power transmission
device; and
a second rectifier circuit that includes a second resistor that is
a current-limiting resistor provided between the coil end node and
a second monitoring node where a waveform-monitoring second induced
voltage signal is generated, a third resistor provided between the
second monitoring node and a low-potential-side power supply node,
and a third diode provided between the second monitoring node and
the low-potential-side power supply node, a forward direction of
the third diode being a direction from the low-potential-side power
supply node to the second monitoring node, the second rectifier
circuit outputting the second induced voltage signal to the power
transmission control device.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIGS. 1A and 1B are views illustrative of non-contact power
transmission.
FIG. 2 shows a configuration example of a power transmission
device, a power transmission control device, a power reception
device, and a power reception control device according to one
embodiment of the invention.
FIG. 3A is a view illustrative of data transfer by means of
frequency modulation, and FIG. 3B is a view illustrative of data
transfer by means of load modulation.
FIG. 4 is a flowchart illustrative of an outline of a
power-transmission-side operation and a power-reception-side
operation.
FIG. 5 shows a first configuration example of a waveform monitoring
circuit according to one embodiment of the invention.
FIG. 6 shows a second configuration example of a waveform
monitoring circuit according to one embodiment of the
invention.
FIG. 7 shows a third configuration example of a waveform monitoring
circuit according to one embodiment of the invention.
FIG. 8 shows a fourth configuration example of a waveform
monitoring circuit according to one embodiment of the
invention.
FIG. 9 shows a signal waveform example illustrative of the
operation of a waveform monitoring circuit.
FIG. 10 shows a signal waveform example illustrative of the
operation of a waveform monitoring circuit.
FIG. 11 shows a fifth configuration example of a waveform
monitoring circuit according to one embodiment of the
invention.
FIG. 12 shows a signal waveform example illustrative of the
operation of a waveform monitoring circuit.
FIG. 13 shows a first configuration example of a power transmission
device according to one embodiment of the invention.
FIGS. 14A to 14C show signal waveform measurement results
illustrative of a first pulse width detection method.
FIG. 15A shows an equivalent circuit in a no-load state, FIG. 15B
shows an equivalent circuit in a load-connected state, and FIG. 15C
is a resonance characteristic diagram in a no-load state and a
load-connected state.
FIG. 16 shows a specific example of a first configuration example
of a power transmission device.
FIG. 17 shows a signal waveform example illustrative of the
operation of a first configuration example of a power transmission
device.
FIG. 18 shows a second configuration example of a power
transmission device according to one embodiment of the
invention.
FIGS. 19A to 19C show signal waveform measurement results
illustrative of a second pulse width detection method.
FIGS. 20A and 20B are views illustrative of a variation in pulse
width detection due to a change in power supply voltage.
FIG. 21 is a flowchart illustrative of primary foreign object
detection and secondary foreign object detection.
FIG. 22 shows a specific example of a second configuration example
of a power transmission device.
FIG. 23 shows a signal waveform example illustrative of the
operation of a second configuration example of a power transmission
device.
FIG. 24 shows a specific configuration example of a third waveform
detection circuit included in a waveform detection circuit.
FIG. 25 shows a signal waveform example illustrative of the
operation of an amplitude detection circuit of the third waveform
detection circuit.
DETAILED DESCRIPTION OF THE EMBODIMENT
Several aspects of the invention may provide a power transmission
device including a waveform monitoring circuit suitable for a
non-contact power transmission system, an electronic instrument,
and the like.
According to one embodiment of the invention, there is provided a
power transmission device included in a non-contact power
transmission system that transmits power to a power reception
device by electromagnetically coupling a primary coil and a
secondary coil to transmit power to a load of the power reception
device, the power transmission device comprising:
a waveform monitoring circuit that generates and outputs a
waveform-monitoring induced voltage signal based on a coil end
signal of the primary coil; and
a power transmission control device that controls a power
transmission driver that drives the primary coil, the power
transmission control device receiving the waveform-monitoring
induced voltage signal and detecting a waveform of the induced
voltage signal to detect a power-reception-side load state,
the waveform monitoring circuit including a first rectifier circuit
having a limiter function, the first rectifier circuit including a
first resistor that is a current-limiting resistor provided between
a coil end node where the coil end signal of the primary coil is
generated and a first monitoring node where a waveform-monitoring
first induced voltage signal is generated, performing a limiter
operation that clamps the first induced voltage signal at a
high-potential-side power supply voltage, and performing a
half-wave rectification of the first induced voltage signal.
According to this embodiment, the waveform monitoring circuit
generates the waveform-monitoring induced voltage signal based on
the coil end signal of the primary coil, and outputs the induced
voltage signal to the power transmission control device. A
situation in which an overcurrent from the coil end node flows into
the power transmission control device can be prevented by the
current control resistor provided in the first rectifier circuit of
the waveform monitoring circuit. Since the first rectifier circuit
of the waveform monitoring circuit clamps the induced voltage
signal at the high-potential-side power supply voltage, a situation
in which a voltage equal to or higher than the maximum rated
voltage is applied to the power transmission control device can be
prevented. Moreover, a situation in which a negative voltage is
applied to the power transmission control device can be prevented
by causing the first rectifier circuit to subject the induced
voltage signal to half-wave rectification.
In the power transmission device according to this embodiment,
the first rectifier circuit may include:
a first diode provided between the first monitoring node and a
high-potential-side power supply node, a forward direction of the
first diode being a direction from the first monitoring node to the
high-potential-side power supply node; and
a second diode provided between the first monitoring node and a
low-potential-side power supply node, a forward direction of the
second diode being a direction from the low-potential-side power
supply node to the first monitoring node.
The limit operation of the first rectifier circuit can be
implemented by providing the first diode, and half-wave
rectification of the first rectifier circuit can be implemented by
providing the second diode.
In the power transmission device according to this embodiment,
the first rectifier circuit may include a Zener diode provided
between the first monitoring node and a low-potential-side power
supply node, a forward direction of the Zener diode being a
direction from the low-potential-side power supply node to the
first monitoring node.
This makes it possible to implement the limit operation without
providing the first diode.
In the power transmission device according to this embodiment,
the first rectifier circuit may include:
a first diode provided between the first monitoring node and a
high-potential-side power supply node, a forward direction of the
first diode being a direction from the first monitoring node to the
high-potential-side power supply node;
a second diode provided between the first monitoring node and a
low-potential-side power supply node, a forward direction of the
second diode being a direction from the low-potential-side power
supply node to the first monitoring node; and
a first capacitor provided between a low-potential-side resistor
end node and the coil end node, the low-potential-side resistor end
node being provided between the first resistor and the second
diode.
According to this configuration, a DC offset component of the coil
end signal can be removed by capacitive coupling of the first
capacitor, whereby an offset-free state of the coil end signal can
be implemented.
In the power transmission device according to this embodiment,
the power transmission control device may include a waveform
detection circuit that detects a change in waveform of the induced
voltage signal of the primary coil;
the waveform detection circuit may include:
a first waveform detection circuit that detects a waveform of the
first induced voltage signal of the primary coil; and
a second waveform detection circuit that detects a waveform of a
second induced voltage signal of the primary coil; and
the waveform monitoring circuit may include:
the first rectifier circuit that outputs the waveform-monitoring
first induced voltage signal to the first waveform detection
circuit through the first monitoring node; and
a second rectifier circuit that outputs the waveform-monitoring
second induced voltage signal to the second waveform detection
circuit through a second monitoring node.
According to this configuration, the first and second induced
voltage signals suitable for the first and second waveform
detection circuits can be generated using the first and second
rectifier circuits.
In the power transmission device according to this embodiment,
the second rectifier circuit may include:
a second resistor provided between the coil end node and the second
monitoring node;
a third resistor provided between the second monitoring node and a
low-potential-side power supply node; and
a third diode provided between the second monitoring node and the
low-potential-side power supply node, a forward direction of the
third diode being a direction from the low-potential-side power
supply node to the second monitoring node.
This enables the second induced voltage signal obtained by reducing
the waveform of the coil end signal to be output to the power
transmission control device.
In the power transmission device according to this embodiment,
the power transmission control device may include:
a drive clock signal generation circuit that generates and outputs
a drive clock signal that specifies a drive frequency of the
primary coil;
a driver control circuit that generates a driver control signal
based on the drive clock signal, and outputs the driver control
signal to the power transmission driver that drives the primary
coil; and
a control circuit that detects the power-reception-side load state
based on a detection result of the waveform detection circuit;
the first waveform detection circuit of the waveform detection
circuit may include a first pulse width detection circuit, when a
timing at which the first induced voltage signal that has changed
from a low-potential-side power supply voltage exceeds a first
threshold voltage is referred to as a first timing, the first pulse
width detection circuit measuring a first pulse width period to
detect first pulse width information, the first pulse width period
being a period between a first edge timing of the drive clock
signal and the first timing; and
the control circuit may detect the power-reception-side load state
based on the first pulse width information.
According to this configuration, the first pulse width period
(i.e., the period between the first edge timing (e.g., falling or
rising edge timing) of the drive clock signal and the first timing)
is measured and detected as the first pulse width information. The
power-reception-side load state is detected based on the detected
first pulse width information. Therefore, a change in
power-reception-side load can be stably detected without employing
a method that separately detects voltage and current and makes a
determination based on the phase difference. Therefore, a change in
secondary-side load can be appropriately detected by a simple
configuration. According to the invention, since the first timing
is set to be a timing at which the first induced voltage signal
that has changed from the low-potential-side power supply voltage
exceeds the first threshold voltage, the pulse width can be
detected with a small variation even if the power supply voltage or
the like has changed.
In the power transmission device according to this embodiment,
the first waveform detection circuit may include a first waveform
adjusting circuit that adjusts a waveform of the first induced
voltage signal and outputs a first waveform-adjusted signal;
and
the first pulse width detection circuit may measure the first pulse
width period based on the first waveform-adjusted signal and the
drive clock signal.
This makes it possible to digitally measure the first pulse width
period using the drive clock signal and a signal of which the
waveform has been adjusted by the first waveform adjusting
circuit.
In the power transmission device according to this embodiment,
the first pulse width detection circuit may include a first counter
that increments or decrements a count value in the first pulse
width period and measures the first pulse width period based on
resulting count value of the first counter.
This makes it possible to more accurately measure the first pulse
width period digitally using the first counter.
In the power transmission device according to this embodiment,
the control circuit may perform primary foreign object detection
based on the first pulse width information, the primary foreign
object detection being foreign object detection before normal power
transmission starts.
According to this configuration, primary foreign object detection
can be implemented in a no-load state before normal power
transmission starts, for example.
In the power transmission device according to this embodiment,
the second waveform detection circuit may include a second pulse
width detection circuit that measures a second pulse width period
and detects second pulse width information, the second pulse width
period being a period between a second edge timing of the drive
clock signal and a second timing, the second timing being a timing
when the second induced voltage signal of the primary coil that has
changed from a high-potential-side power supply voltage falls below
a second threshold voltage; and
the control circuit may perform secondary foreign object detection
based on the second pulse width information, the secondary foreign
object detection being foreign object detection after normal power
transmission has started.
According to this configuration, since a foreign object can be
detected by a different standard before and after normal power
transmission, foreign object detection accuracy and stability can
be improved.
In the power transmission device according to this embodiment,
the second waveform detection circuit may include a second waveform
adjusting circuit that adjusts a waveform of the second induced
voltage signal and outputs a second waveform-adjusted signal;
and
the second pulse width detection circuit may measure the second
pulse width period based on the second waveform-adjusted signal and
the drive clock signal.
This makes it possible to digitally measure the second pulse width
period using the drive clock signal and a signal of which the
waveform has been adjusted by the second waveform adjusting
circuit.
In the power transmission device according to this embodiment,
the second pulse width detection circuit may include a second
counter that increments or decrements a count value in the second
pulse width period and measures the second pulse width period based
on resulting count value of the second counter.
This makes it possible to more accurately measure the second pulse
width period digitally using the second counter.
In the power transmission control device according to this
embodiment,
the first waveform detection circuit may include a first waveform
adjusting circuit that adjusts a waveform of the first induced
voltage signal and outputs a first waveform-adjusted signal to the
first pulse width detection circuit; and
the second waveform adjusting circuit may adjust a waveform of the
second induced voltage signal differing from the first induced
voltage signal, and outputting the second waveform-adjusted signal
to the second pulse width detection circuit.
According to this configuration, the pulse width can be detected
using the first and second induced voltage signals that differ in
signal state between a first method that utilizes the first
waveform adjusting circuit and the first pulse width detection
circuit, and a second method that utilizes the second waveform
adjusting circuit and the second pulse width detection circuit.
Therefore, pulse width detection accuracy and stability can be
improved.
In the power transmission device according to this embodiment,
the power transmission control device may include a waveform
detection circuit that detects a change in waveform of the induced
voltage signal of the primary coil;
the waveform detection circuit may include:
a first waveform detection circuit that detects a waveform of the
first induced voltage signal of the primary coil; and
a second waveform detection circuit that detects a waveform of a
second induced voltage signal of the primary coil;
the waveform monitoring circuit may include:
the first rectifier circuit that outputs the waveform-monitoring
first induced voltage signal to the first waveform detection
circuit through the first monitoring node; and
a second rectifier circuit that outputs the waveform-monitoring
second induced voltage signal to the second waveform detection
circuit through a second monitoring node;
the first rectifier circuit may include:
a first diode provided between the first monitoring node and a
high-potential-side power supply node, a forward direction of the
first diode being a direction from the first monitoring node to the
high-potential-side power supply node;
a second diode provided between the first monitoring node and a
low-potential-side power supply node, a forward direction of the
second diode being a direction from the low-potential-side power
supply node to the first monitoring node; and
a first capacitor provided between a low-potential-side resistor
end node and the coil end node, the low-potential-side resistor end
node being provided between the first resistor and the second
diode; and
the second rectifier circuit may include:
a third diode provided between the second monitoring node and a
high-potential-side power supply node, a forward direction of the
third diode being a direction from the second monitoring node to
the high-potential-side power supply node;
a fourth diode provided between the second monitoring node and a
low-potential-side power supply node, a forward direction of the
fourth diode being a direction from the low-potential-side power
supply node to the second monitoring node;
a second resistor provided between the third diode and the second
monitoring node; a third resistor provided between the second
monitoring node and the low-potential-side power supply node;
and
a second capacitor provided between a high-potential-side resistor
end node and the coil end node, the high-potential-side resistor
end node being provided between the third diode and the second
resistor.
According to this configuration, a DC offset of the coil end signal
can be removed by providing the first and second capacitors,
whereby an offset-free state of the coil end signal can be
implemented.
In the power transmission device according to this embodiment,
the power transmission control device may include:
a drive clock signal generation circuit that generates and outputs
a drive clock signal that specifies a drive frequency of the
primary coil;
a driver control circuit that generates a driver control signal
based on the drive clock signal, and outputs the driver control
signal to the power transmission driver that drives the primary
coil; and
a control circuit that detects the power-reception-side load state
based on a detection result of the waveform detection circuit;
and
the first waveform detection circuit of the waveform detection
circuit may include a first pulse width detection circuit, when a
timing at which the first induced voltage signal that has changed
from a low-potential-side power supply voltage exceeds a first
threshold voltage is referred to as a first timing, the first pulse
width detection circuit measuring a first pulse width period to
detect first pulse width information, the first pulse width period
being a period between a first edge timing of the drive clock
signal and the first timing.
According to this configuration, a change in power-reception-side
load can be stably detected without employing a method that
separately detects voltage and current and makes a determination
based on the phase difference. Therefore, a change in
secondary-side load can be appropriately detected by a simple
configuration. According to the invention, since the first timing
is set to be a timing at which the first induced voltage signal
that has changed from the low-potential-side power supply voltage
exceeds the first threshold voltage, the pulse width can be
detected with a small variation even if the power supply voltage or
the like has changed.
In the power transmission device according to this embodiment,
the second waveform detection circuit may include a second pulse
width detection circuit that measures a second pulse width period
and detects second pulse width information, the second pulse width
period being a period between a second edge timing of the drive
clock signal and a second timing, the second timing being a timing
when the second induced voltage signal of the primary coil that has
changed from a high-potential-side power supply voltage falls below
a second threshold voltage.
This makes it possible to reduce the waveform of the coil end
signal and compare the voltage level of the second induced voltage
signal obtained by reducing the waveform of the coil end signal
with the second threshold voltage to obtain the second pulse width
information.
According to another embodiment of the invention, there is provided
an electronic instrument comprising one of the above power
transmission devices.
According to another embodiment of the invention, there is provided
a waveform monitoring circuit provided in a power transmission
device included in a non-contact power transmission system that
transmits power to a power reception device by electromagnetically
coupling a primary coil and a secondary coil to transmit power to a
load of the power reception device, the waveform monitoring circuit
comprising:
a first rectifier circuit having a limiter function, the first
rectifier circuit including a first resistor that is a
current-limiting resistor provided between a coil end node where a
coil end signal of the primary coil is generated and a first
monitoring node where a waveform-monitoring first induced voltage
signal is generated, performing a limiter operation that clamps the
first induced voltage signal at a high-potential-side power supply
voltage, performing a half-wave rectification of the first induced
voltage signal, and outputting the first induced voltage signal to
a power transmission control device of the power transmission
device; and
a second rectifier circuit that includes a second resistor that is
a current-limiting resistor provided between the coil end node and
a second monitoring node where a waveform-monitoring second induced
voltage signal is generated, a third resistor provided between the
second monitoring node and a low-potential-side power supply node,
and a third diode provided between the second monitoring node and
the low-potential-side power supply node, a forward direction of
the third diode being a direction from the low-potential-side power
supply node to the second monitoring node, the second rectifier
circuit outputting the second induced voltage signal to the power
transmission control device.
Preferred embodiments of the invention are described in detail
below. Note that the following embodiments do not in any way limit
the scope of the invention defined by the claims laid out herein.
Note that all elements of the following embodiments should not
necessarily be taken as essential requirements for the
invention.
1. Electronic Instrument
FIG. 1A shows examples of an electronic instrument to which a
non-contact power transmission method according to one embodiment
of the invention is applied. A charger 500 (cradle) (i.e.,
electronic instrument) includes a power transmission device 10. A
portable telephone 510 (i.e., electronic instrument) includes a
power reception device 40. The portable telephone 510 also includes
a display section 512 (e.g., LCD), an operation section 514 that
includes a button or the like, a microphone 516 (sound input
section), a speaker 518 (sound output section), and an antenna
520.
Power is supplied to the charger 500 through an AC adaptor 502. The
power supplied to the charger 500 is transmitted from the power
transmission device 10 to the power reception device 40 by means of
non-contact power transmission. This makes it possible to charge a
battery of the portable telephone 510 or operate a device provided
in the portable telephone 510.
Note that the electronic instrument to which this embodiment is
applied is not limited to the portable telephone 510. For example,
this embodiment may be applied to various electronic instruments
such as a wristwatch, a cordless telephone, a shaver, an electric
toothbrush, a wrist computer, a handy terminal, a portable
information terminal, a power-assisted bicycle, and an IC card.
As schematically shown in FIG. 1B, power transmission from the
power transmission device 10 to the power reception device 40 is
implemented by electromagnetically coupling a primary coil L1
(power-transmission-side coil) provided in the power transmission
device 10 and a secondary coil L2 (power-reception-side coil)
provided in the power reception device 40 to form a power
transmission transformer. This enables non-contact power
transmission.
2. Power Transmission Device and Power Reception Device
FIG. 2 shows a configuration example of the power transmission
device 10, a power transmission control device 20, the power
reception device 40, and a power reception control device 50
according to this embodiment. A power-transmission-side electronic
instrument such as the charger 500 shown in FIG. 1A includes the
power transmission device 10 shown in FIG. 2. A
power-reception-side electronic instrument such as the portable
telephone 510 may include the power reception device 40 and a load
90 (actual load). The configuration shown in FIG. 2 implements a
non-contact power transmission (contactless power transmission)
system that transmits power from the power transmission device 10
to the power reception device 40 by electromagnetically coupling
the primary coil L1 and the secondary coil L2 (e.g., planar coil),
and supplies power (voltage VOUT) to the load 90 from a voltage
output node NB7 of the power reception device 40.
The power transmission device 10 (power transmission module or
primary module) may include the primary coil L1, a power
transmission section 12, a waveform monitoring circuit 14, a
display section 16, and the power transmission control device 20.
The power transmission device 10 and the power transmission control
device 20 are not limited to the configuration shown in FIG. 2.
Various modifications may be made such as omitting some of the
elements (e.g., display section or waveform monitoring circuit),
adding other elements, or changing the connection relationship.
The power transmission section 12 generates an alternating-current
voltage at a given frequency during power transmission, and
generates an alternating-current voltage at a frequency that
differs depending on data during data transfer. The power
transmission section 12 supplies the generated alternating-current
voltage to the primary coil L1. As shown in FIG. 3A, the power
transmission section 12 generates an alternating-current voltage at
a frequency f1 when transmitting data "1" to the power reception
device 40, and generates an alternating-current voltage at a
frequency f2 when transmitting data "0" to the power reception
device 40, for example. The power transmission section 12 may
include a first power transmission driver that drives one end of
the primary coil L1, a second power transmission driver that drives
the other end of the primary coil L1, and at least one capacitor
that forms a resonant circuit together with the primary coil
L1.
Each of the first and second power transmission drivers included in
the power transmission section 12 is an inverter circuit (buffer
circuit) that includes a power MOS transistor, for example, and is
controlled by a driver control circuit 26 of the power transmission
control device 20.
The primary coil L1 (power-transmission-side coil) is
electromagnetically coupled with the secondary coil L2
(power-reception-side coil) to form a power transmission
transformer. For example, when power transmission is necessary, the
portable telephone 510 is placed on the charger 500 so that a
magnetic flux of the primary coil L1 passes through the secondary
coil L2, as shown in FIGS. 1A and 1B. When power transmission is
unnecessary, the charger 500 and the portable telephone 510 are
physically separated so that a magnetic flux of the primary coil L1
does not pass through the secondary coil L2.
The waveform monitoring circuit 14 (rectifier circuit or waveform
adjusting circuit) generates a waveform-monitoring induced voltage
signal PHIN based on a coil end signal CSG of the primary coil L1.
For example, the coil end signal CSG (induced voltage signal) of
the primary coil L1 may exceed the maximum rated voltage of an IC
of the power transmission control device 20, or may be set at a
negative voltage. The waveform monitoring circuit 14 receives the
coil end signal CSG, generates a waveform-monitoring induced
voltage signal PHIN of which the waveform can be detected by a
waveform detection circuit 30 of the power transmission control
device 20, and outputs the induced voltage signal PHIN to a
waveform-monitoring terminal of the power transmission control
device 20, for example. The detail of the waveform monitoring
circuit 14 is described later.
The display section 16 displays the state (e.g., power transmission
or ID authentication) of the non-contact power transmission system
using a color, an image, or the like. The display section 16 is
implemented by an LED, an LCD, or the like.
The power transmission control device 20 controls the power
transmission device 10. The power transmission control device 20
may be implemented by an integrated circuit device (IC) or the
like. The power transmission control device 20 may include a
(power-transmission-side) control circuit 22, an oscillation
circuit 24, a drive clock signal generation circuit 25, a driver
control circuit 26, and the waveform detection circuit 30. Note
that modifications may be made such as omitting some of the
elements or adding other elements.
The power-transmission-side control circuit 22 (control section)
controls the power transmission device 10 and the power
transmission control device 20. The control circuit 22 may be
implemented by a gate array, a microcomputer, or the like.
Specifically, the control circuit 22 performs sequence control and
a determination process necessary for power transmission, load
state detection (e.g., data detection, foreign object detection,
and removal detection), frequency modulation, and the like.
The oscillation circuit 24 includes a crystal oscillation circuit,
for example. The oscillation circuit 24 generates a primary-side
clock signal. The drive clock signal generation circuit 25
generates a drive clock signal that specifies a drive frequency.
The driver control circuit 26 generates a control signal at a
desired frequency based on the drive clock signal, a frequency
setting signal from the control circuit 22, and the like, and
outputs the generated control signal to the first and second power
transmission drivers of the power transmission section 12 to
control the first and second power transmission drivers.
The waveform detection circuit 30 detects a change in waveform of
the induced voltage signal PHIN of the primary coil L1. For
example, when the load state (load current) of the
power-reception-side instrument (secondary-side instrument) has
changed, the waveform of the induced voltage signal PHIN changes.
The waveform detection circuit 30 detects such a change in
waveform, and outputs the detection result (detection result
information) to the control circuit 22.
Specifically, the waveform detection circuit 30 adjusts the
waveform of the induced voltage signal PHIN, and generates a
waveform-adjusted signal. For example, the waveform detection
circuit 30 generates a square wave (rectangular wave)
waveform-adjusted signal that becomes active (e.g., H level) when
the induced voltage signal PHIN has exceeded a given threshold
voltage. The waveform detection circuit 30 detects pulse width
information (pulse width period) relating to the waveform-adjusted
signal based on the waveform-adjusted signal and the drive clock
signal. Specifically, the waveform detection circuit 30 receives
the waveform-adjusted signal and the drive clock signal from the
drive clock signal generation circuit 25, and detects the pulse
width information relating to the waveform-adjusted signal to
detect pulse width information relating to the induced voltage
signal PHIN.
The control circuit 22 detects the load state (change in load or
degree of load) of the power-reception-side instrument (power
reception device 40) based on the detection result of the waveform
detection circuit 30. Specifically, the control circuit 22 detects
the power-reception-side load state based on the pulse width
information detected by the waveform detection circuit 30 (pulse
width detection circuit), and performs data (load) detection,
foreign object (metal) detection, removal (detachment) detection,
and the like. The pulse width period that is the pulse width
information relating to the induced voltage signal changes
corresponding to the power-reception-side load. The control circuit
22 detects a change in the power-reception-side load based on the
pulse width period (i.e., a count value obtained by measuring the
pulse width period). Therefore, when a load modulation section 46
of the power reception device 40 has transmitted data by means of
load modulation (see FIG. 3B), the transmitted data can be
detected.
The power reception device 40 (power reception module or secondary
module) may include the secondary coil L2, the power reception
section 42, the load modulation section 46, a power supply control
section 48, and the power reception control device 50. Note that
the power reception device 40 and the power reception control
device 50 are not limited to the configuration shown in FIG. 2.
Various modifications may be made such as omitting some of the
elements, adding other elements, or chancing the connection
relationship.
The power reception section 42 converts an alternating-current
induced voltage in the secondary coil L2 into a direct-current
voltage. A rectifier circuit 43 included in the power reception
section 42 converts the alternating-current induced voltage. The
rectifier circuit 43 includes diodes DB1 to DB4. The diode DB1 is
provided between a node NB1 at one end of the secondary coil L2 and
a node NB3 (direct-current voltage VDC generation node). The diode
DB2 is provided between the node NB3 and a node NB2 at the other
end of the secondary coil L2. The diode DB3 is provided between the
node NB2 and a node NB4 (VSS). The diode DB4 is provided between
the nodes NB4 and NB1.
Resistors RB1 and RB2 of the power reception section 42 are
provided between the nodes NB1 and NB4. A signal CCMPI obtained by
dividing the voltage between the nodes NB1 and NB4 using the
resistors RB1 and RB2 is input to a frequency detection circuit 60
of the power reception control device 50.
A capacitor CB1 and resistors RB4 and RB5 of the power reception
section 42 are provided between the node NB3 (direct-current
voltage VDC) and the node NB4 (VSS). A signal ADIN obtained by
dividing the voltage between the nodes NB3 and NB4 using the
resistors RB4 and RB5 is input to a position detection circuit 56
of the power reception control device 50.
The load modulation section 46 performs a load modulation process.
Specifically, when the power reception device 40 transmits desired
data to the power transmission device 10, the load modulation
section 46 variably changes the load of the load modulation section
46 (secondary-side instrument) corresponding to transmission data
to chance the signal waveform of the induced voltage in the primary
coil L1 as shown in FIG. 3B. The load modulation section 46
includes a resistor RB3 and a transistor TB3 (N-type CMOS
transistor) provided in series between the nodes NB3 and NB4. The
transistor TB3 is ON/OFF-controlled based on a signal P3Q from a
control circuit 52 of the power reception control device 50. When
the load modulation section 46 performs load modulation by
ON/OFF-controlling the transistor TB3, a transistor TB2 of the
power supply control section 48 is turned OFF so that the load 90
is electrically disconnected from the power reception device
40.
For example, when reducing the secondary-side load (high impedance)
in order to transmit data "0" (see FIG. 3B), the signal P3Q is set
at the L level so that the transistor TB3 is turned OFF. As a
results the load of the load modulation section 46 becomes almost
infinite (no load). On the other hand, when increasing the
secondary-side load (low impedance) in order to transmit data "1",
the signal P3Q is set at the H level so that the transistor TB3 is
turned ON. As a result, the load of the load modulation section 46
is equivalent to the resistor RB3 (high load).
The power supply control section 48 controls the amount of power
supplied to the load 90. A regulator 49 regulates the voltage level
of the direct-current voltage VDC obtained by conversion by the
rectifier circuit 43 to generate a power supply voltage VD5 (e.g.,
5 V). The power reception control device 50 operates based on the
power supply voltage VD5 supplied from the power supply control
section 48, for example.
The transistor TB2 (P-type CMOS transistor) is controlled based on
a signal P1Q from the control circuit 52 of the power reception
control device 50. Specifically, the transistor TB2 is turned ON
when normal power transmission is performed after ID authentication
has been completed (established), and is turned OFF during load
modulation or the like.
The power reception control device 50 controls the power reception
device 40. The power reception control device 50 may be implemented
by an integrated circuit device (IC) or the like. The power
reception control device 50 may operate based on the power supply
voltage VD5 generated based on the induced voltage in the secondary
coil L2. The power reception control device 50 may include the
(power-reception-side) control circuit 52, the position detection
circuit 56, an oscillation circuit 58, the frequency detection
circuit 60, and a full-charge detection circuit 62.
The control circuit 52 (control section) controls the power
reception device 40 and the power reception control device 50. The
control circuit 52 may be implemented by a gate array, a
microcomputer, or the like. Specifically, the control circuit 22
performs sequence control and a determination process necessary for
ID authentication, position detection, frequency detection, load
modulation, full-charge detection, and the like.
The position detection circuit 56 monitors the waveform of the
signal ADIN that corresponds to the waveform of the induced voltage
in the secondary coil L2, and determines whether or not the
positional relationship between the primary coil L1 and the
secondary coil L2 is appropriate. Specifically, the position
detection circuit 56 converts the signal ADIN into a binary value
using a comparator or determines the level of the signal ADIN by
A/D conversion, and determines whether or not the positional
relationship between the primary coil L1 and the secondary coil L2
is appropriate.
The oscillation circuit 58 includes a CR oscillation circuit or the
like, and generates a secondary-side clock signal. The frequency
detection circuit 60 detects the frequency (f1 or f2) of the signal
CCMPI, and determines whether the data transmitted from the power
transmission device 10 is "1" or "0", as shown in FIG. 3A.
The full-charge detection circuit 62 (charge detection circuit) is
a circuit that detects whether or not a battery 94 (secondary
battery) of the load 90 has been fully charged (charged).
The load 90 may include a charge control device 92 that controls
charging of the battery 94 and the like. The charge control device
92 (charge control IC) may be implemented by an integrated circuit
device or the like. The battery 94 may be provided with the
function of the charge control device 92 (e.g., smart battery).
An outline of the power-transmission-side operation and the
power-reception-side operation is described below using a flowchart
shown in FIG. 4. When power has been supplied to the
power-transmission-side instrument (step S1), the
power-transmission-side instrument performs temporary power
transmission for position detection (step S2). The
power-reception-side power supply voltage rises due to power
transmission so that the reset state of the power reception control
device 50 is canceled (step S11). The power-reception-side
instrument then sets the signal P1Q at the H level (step S12). This
causes the transistor TB2 to be turned OFF so that the load 90 is
electrically disconnected from the power reception device 40.
The power-reception-side instrument then determines whether or not
the positional relationship between the primary coil L1 and the
secondary coil L2 is appropriate using the position detection
circuit 56 (step S13). When the power-reception-side instrument has
determined that the positional relationship between the primary
coil L1 and the secondary coil L2 is appropriate, the
power-reception-side instrument starts an ID authentication process
and transmits an authentication frame to the
power-transmission-side instrument (step S14). Specifically, the
power-reception-side instrument transmits data relating to the
authentication frame by means of load modulation described with
reference to FIG. 3B.
When the power-transmission-side instrument has received the
authentication frame, the power-transmission-side instrument
performs the ID determination process or the like (step S3). When
the power-transmission-side instrument accepts the ID
authentication, the power-transmission-side instrument transmits an
acceptance frame to the power-reception-side instrument (step S4).
Specifically, the power-transmission-side instrument transmits data
by means of frequency modulation described with reference to FIG.
3A.
The power-reception-side instrument receives the acceptance frame.
When the acceptance frame indicates OK, the power-reception-side
instrument transmits a start frame for starting non-contact power
transmission to the power-transmission-side instrument (steps S15
and S16). The power-transmission-side instrument receives the start
frame. When the start frame indicates OK, the
power-transmission-side instrument starts normal power transmission
(steps S5 and S6). The power-reception-side instrument sets the
signal P1Q at the L level (step S17). This causes the transistor
TB2 to be turned ON so that power can be transmitted to the load
90. Power is then supplied to the load (i.e., the voltage VOUT is
output to the load) (step S18).
3. Waveform Monitoring Circuit
3.1 First Configuration Example
FIG. 5 shows a first configuration example of the waveform
monitoring circuit 14 according to this embodiment. In FIG. 5, the
power transmission control device 20 controls the power
transmission drivers (first and second power transmission drivers)
of the power transmission section 12 that drives the primary coil
L1. The power transmission control device 20 receives a
waveform-monitoring induced voltage signal PHIN1 from the waveform
monitoring circuit 14 through a waveform monitor terminal. The
waveform detection circuit 30 included in the power transmission
control device 20 detects a change in waveform of the induced
voltage signal PHIN1 to detect the power-reception-side
(secondary-side) load state.
The waveform monitoring circuit 14 generates the
waveform-monitoring induced voltage signal PHIN1 based on a coil
end signal CSG of the primary coil L1, and outputs the induced
voltage signal PHIN1 to the power transmission control device 20.
Specifically, the waveform monitoring circuit 14 includes a first
rectifier circuit 17 having a limiter function. The rectifier
circuit 17 includes a first resistor (current-limiting resistor)
RA1 provided between a coil end node NA2 at which the coil end
signal CSG of the primary coil L1 is generated and a first
monitoring node NA11 at which the waveform-monitoring induced
voltage signal PHIN1 is generated. The rectifier circuit 17
performs a limiter operation that clamps the induced voltage signal
PHIN1 at a voltage VDD (high-potential-side power supply voltage),
and subjects the induced voltage signal PHIN1 to half-wave
rectification.
A situation in which an overcurrent from the coil end node NA2
flows into an IC terminal of the power transmission control device
20 is prevented by providing the current-limiting resistor RA1. A
situation in which a voltage equal to or higher than the maximum
rated voltage is applied to the IC terminal of the power
transmission control device 20 is also prevented by causing the
rectifier circuit 17 to clamp the induced voltage signal PHIN1 at
the voltage VDD. Moreover, a situation in which a negative voltage
is applied to the IC terminal of the power transmission control
device 20 is prevented by causing the rectifier circuit 17 to
subject the induced voltage signal PHIN1 to half-wave
rectification.
Specifically, the rectifier circuit 17 includes a first diode DA1
provided between the monitoring node NA11 and a VDD
(high-potential-side power supply in a broad sense) node, the
forward direction of the first diode DA1 being a direction from the
monitoring node NA11 to the VDD node. The rectifier circuit 17 also
includes a second diode DA2 provided between the monitoring node
NA11 and a GND (low-potential-side power supply in a broad sense)
node, the forward direction of the second diode DA2 being a
direction from the GND node to the monitoring node NA11. The VDD
limit operation is implemented using the diode DA1, and half-wave
rectification is implemented using the diode DA2.
3.2 Second Configuration Example
FIG. 6 shows a second configuration example of the waveform
monitoring circuit 14. In the second configuration example, a Zener
diode DZ1 is provided in the rectifier circuit 17 instead of the
diode DA1 shown in FIG. 5. Specifically, the Zener diode is
provided between the monitoring node NA11 and the GND
(low-potential-side power supply) node, the forward direction of
the Zener diode being a direction from the GND node to the
monitoring node NA11.
3.3 Third Configuration Example
FIG. 7 shows a third configuration example of the waveform
monitoring circuit 14. In the third configuration example, the
waveform monitoring circuit 14 includes the first rectifier circuit
17 having a limiter function in the same manner as in the first
configuration example. The rectifier circuit 17 performs a limiter
operation that clamps the induced voltage signal PHIN1 at the
voltage VDD (high-potential-side power supply voltage), and
subjects the induced voltage signal PHIN1 to half-wave
rectification. Specifically, a situation in which a voltage equal
to or higher than the maximum rated voltage is applied to the IC
terminal of the power transmission control device 20 is also
prevented by causing the rectifier circuit 17 to clamp the induced
voltage signal PHIN1 at the voltage VDD. Moreover, a situation in
which a negative voltage is applied to the IC terminal of the power
transmission control device 20 is prevented by causing the
rectifier circuit 17 to subject the induced voltage signal PHIN1 to
half-wave rectification.
Specifically, the rectifier circuit 17 includes a first diode DA1
and a second diode DA2. The first diode DA1 is provided between the
monitoring node NA11 and a VDD node (high-potential-side power
supply node in a broad sense), the forward direction of the first
diode DA1 being a direction from the monitoring node NA11 to the
VDD node. The second diode DA2 is provided between the monitoring
node NA11 and a GND node (low-potential-side power supply node in a
broad sense), the forward direction of the second diode DA2 being a
direction from the GND node to the monitoring node NA11. The VDD
limit operation is implemented using the first diode DA1, and
half-wave rectification is implemented using the second diode
DA2.
A first resistor RA1 (i.e., current-limiting resistor) is provided
between the coil end node NA2 and the first monitoring node NA11 in
order to prevent a situation in which an overcurrent from the coil
end node NA2 flows into an IC terminal of the power transmission
control device 20. In the third configuration example, the first
resistor RA1 is disposed between the first diode DA1 and the second
diode DA2, differing from the first configuration example.
In the third configuration example, a first capacitor CA1 is
provided in the input stage of the rectifier circuit 17.
Specifically, the first capacitor CA1 is provided between the coil
end node NA2 and a low-potential-side resistor end node NA12
between the first resistor RA1 and the second diode DA2.
The coil end signal CSG may have a DC offset (i.e., the center
voltage is not 0 V). A variation in pulse width of a pulse signal
obtained by adjusting the waveform of the induced voltage signal
PHIN1 or the like occurs when the DC offset changes, whereby the
load state detection accuracy deteriorates. In the third
configuration example, the first capacitor CA1 is provided in the
input stage of the rectifier circuit 17 in order to cancel such a
DC offset. An adverse effect of a change in DC offset of the coil
end signal on the load state detection accuracy can be prevented by
extracting only the AC component of the coil end signal by
capacitive coupling of the first capacitor CA1. Moreover, the
voltage level of the coil end signal can be shifted to a voltage
level with high detection sensitivity that enables detection using
a desired threshold voltage. Therefore, the detection accuracy for
the pulse width of a pulse signal obtained by adjusting the
waveform of the induced voltage signal PHIN1 output from the
rectifier circuit 17 or the like is improved, whereby the load
state can be detected with high sensitivity and a high dynamic
range, for example.
3.4 Fourth Configuration Example
FIG. 8 shows a fourth configuration example of the waveform
monitoring circuit 14. In FIG. 8, the waveform monitoring circuit
14 includes a second rectifier circuit 18 in addition to the first
rectifier circuit 17. The waveform detection circuit 30 includes a
first waveform detection circuit 31 and a second waveform detection
circuit 34. The first waveform detection circuit 31 detects a
change in waveform of the first induced voltage signal PHIN1 of the
primary coil L1. The second waveform detection circuit 34 detects a
chance in waveform of a second induced voltage signal PHIN2 of the
primary coil L1.
The second rectifier circuit 18 outputs the waveform-monitoring
second induced voltage signal PHIN2 to the second waveform
detection circuit 34 through a second monitoring node NA21.
Specifically, the rectifier circuit 18 includes a second resistor
RA2 (i.e., current-limiting resistor) provided between the coil end
node NA2 and the monitoring node NA21, and a third resistor RA3
provided between the monitoring node NA21 and a GND
(low-potential-side power supply) node. The rectifier circuit 18
also includes a third diode DA3 provided between the monitoring
node NA21 and the GND node. The voltage of the coil end signal CSG
is divided by the resistors RA2 and RA3, and the divided voltage is
input to the second waveform detection circuit 34 as the induced
voltage signal PHIN2. The diode DA3 subjects the coil end signal
CSG to half-wave rectification so that a negative voltage is not
applied to the second waveform detection circuit 34.
FIG. 9 shows a waveform example of the coil end signal CSG input to
the rectifier circuit 17, the induced voltage signal PHIN1 output
to the first waveform detection circuit 31 from the rectifier
circuit 17, and a pulse signal PLS1 used for pulse width
detection.
As indicated by E1 in FIG. 9, the first waveform detection circuit
31 detects a pulse width period XTPW1 that corresponds to a change
in phase when the induced voltage signal PHIN1 (coil end signal
CSG) rises. Specifically, the first waveform detection circuit 31
measures the pulse width period XTPW1 that is a period between the
timing at which the induced voltage signal PHIN1 that has changed
from 0 V exceeds a threshold voltage VT1 (see E2) and the edge
timing (the rising edge timing in FIG. 9, but may be the falling
edge timing) of the drive clock signal DRCK. In this case, since it
suffices that a voltage near 0 V be detected, the waveform need not
be reduced. Therefore, voltage division using the resistors RA2 and
RA3 of the rectifier circuit 18 shown in FIG. 8 is unnecessary.
This prevents a situation in which the waveform of the signal PHIN1
is deformed or the signal deteriorates due to a resistance division
node and a parasitic capacitor. Therefore, since the first waveform
detection circuit 31 can detect the waveform using the signal PHIN1
having a fine waveform, the detection accuracy can be improved.
When the waveform is not reduced by voltage division using
resistors, the signal PHIN1 may exceed the maximum rated voltage of
the power transmission control device 20. However, since the diode
DA1 is provided in the rectifier circuit 17 and performs the limit
operation that clamps the signal PHIN1 at the voltage VDD (E3), a
situation in which the signal PHIN1 exceeds the maximum rated
voltage can be prevented. Moreover, since the diode DA2 is provided
in the rectifier circuit 17 and performs half-wave rectification
(see E4), a situation in which a negative voltage is applied to the
IC terminal of the power transmission control device 20 can be
prevented.
FIG. 10 shows a waveform example of the coil end signal CSG input
to the rectifier circuit 18, the induced voltage signal PHIN2
output to the second waveform detection circuit 34 from the
rectifier circuit 18, and a pulse signal PLS2 used for pulse width
detection.
As indicated by G1 in FIG. 10, the second waveform detection
circuit 34 detects a pulse width period XTPW2 that corresponds to a
change in phase when the induced voltage signal PHIN2 (coil end
signal CSG) falls. Specifically, the second waveform detection
circuit 34 measures the pulse width period XTPW2 that is a period
between the timing at which the induced voltage signal PHIN2 that
has changed from the voltage VDD becomes lower than a threshold
voltage VT2 (see G2) and the edge timing (the falling edge timing
in FIG. 10, but may be the rising edge timing) of the drive clock
signal DRCK. Therefore, since it is necessary to reduce the
waveform of the coil end signal CSG that exceeds the voltage VDD,
the rectifier circuit 18 performs voltage division using the
resistors RA2 and RA3. Specifically, the threshold voltage of an
N-type transistor can be used as the threshold voltage VT2 by
reducing the waveform of the coil end signal CSG by dividing the
voltage of the coil end signal CSG, for example. Since the diode
DA3 is provided in the rectifier circuit 18 and performs half-wave
rectification (see G3), a situation in which a negative voltage is
applied to the IC terminal of the power transmission control device
20 can be prevented.
For example, when the induced voltage signal PHIN1 input to the
first waveform detection circuit 31 shown in FIG. 8 is generated
using, the rectifier circuit 18 instead of the rectifier circuit
17, the waveform of the induced voltage signal PHIN1 is reduced by
voltage division. Therefore, the waveform is deformed near the
threshold voltage VT1, whereby the detection accuracy may
deteriorate.
In FIG. 8, since the induced voltage signal PHIN1 is generated
using the rectifier circuit 17 that does not perform voltage
division, such a situation can be prevented.
When the limit operation using the diode DA1 of the rectifier
circuit 17 is performed, as indicated by E3 in FIG. 9, the VDD
limit operation of the rectifier circuit 17 adversely affects the
rectifier circuit 18 when the current-limiting resistor RA1 is not
provided between the monitoring node NA11 and the coil end node NA2
shown in FIG. 8B. Specifically, when the current-limiting resistor
RA1 is not provided, the voltage of the coil end node NA2 is
clamped at the voltage VDD due to the limit operation of the
rectifier circuit 17, whereby the operations of the power
transmission driver and the rectifier circuit 18 are adversely
affected.
In FIG. 8, since the current-limiting resistor RA1 is provided
between the coil end node NA2 and the monitoring node NA11, a
situation in which the VDD limit operation (see E3 in FIG. 9) of
the rectifier circuit 17 adversely affects the rectifier circuit 18
can be prevented.
In FIG. 8, circuits (i.e., rectifier circuits 17 and 18) having
different configurations are used as the circuits that generate the
induced voltage signals PHIN1 and PHIN2 for the first and second
waveform detection circuits 31 and 34, as described above. The
dynamic range and the sensitivity complement each other by
selectively utilizing the rectifier circuits 17 and 18, so waveform
detection (pulse width detection) with high accuracy can be
implemented.
3.5 Fifth Configuration Example
FIG. 11 shows a fifth configuration example of the waveform
monitoring circuit 14. In FIG. 11, the waveform monitoring circuit
14 includes a second rectifier circuit 181 and a third rectifier
circuit 191 in addition to the first rectifier circuit 17. The
waveform detection circuit 30 includes the first waveform detection
circuit 31, the second waveform detection circuit 34, and a third
waveform detection circuit 37. The first waveform detection circuit
31 detects a change in waveform of the first induced voltage signal
PHIN1 of the primary coil L1. The second waveform detection circuit
34 detects a change in waveform of the second induced voltage
signal PHIN2 of the primary coil L1. The third waveform detection
circuit 37 detects a change in waveform of a third induced voltage
signal PHIN3 of the primary coil L1.
The first rectifier circuit 17 outputs the waveform-monitoring
first induced voltage signal PHIN1 to the first waveform detection
circuit 31 through the first monitoring node NA11. The
configuration of the first rectifier circuit 17 is similar to that
of the rectifier circuit included in the third configuration
example of the waveform monitoring circuit 14 shown in FIG. 7.
Specifically, the first rectifier circuit 17 includes the first
diode DA1 provided between the monitoring node NA11 and the VDD
node, and the second diode DA2 provided between the monitoring node
NA11 and the GND node. The VDD limit operation is implemented using
the first diode DA1, and half-wave rectification is implemented
using the second diode DA2.
The first resistor RA1 (i.e., current-limiting resistor) is
provided between the coil end node NA2 and the first monitoring
node NA11 in order to prevent a situation in which an overcurrent
from the coil end node NA2 flows into the IC terminal of the power
transmission control device 20. Specifically, the first resistor
RA1 is disposed between the first diode DA1 and the second diode
DA2. The first capacitor CA1 is provided in the input stage of the
first rectifier circuit 17 (i.e., between the coil end node NA2 and
the low-potential-side resistor end node NA12 between the first
resistor RA1 and the second diode DA2).
The second rectifier circuit 181 outputs the waveform-monitoring
second induced voltage signal PHIN2 to the second waveform
detection circuit 34 through the second monitoring node NA21. The
second rectifier circuit 181 includes a third diode DA3B provided
between the second monitoring node NA21 and the GND node, and a
fourth diode DA4B provided between the second monitoring node NA21
and the VDD node. In the second rectifier circuit 181, the VDD
limit operation is implemented using the fourth diode DA4B, and
half-wave rectification is implemented using the third diode
DA3B.
In order to prevent a situation in which an overcurrent from the
coil end node NA2 flows into the IC terminal of the power
transmission control device 20, a second resistor RA2B (i.e.,
current-limiting resistor) is provided between the coil end node
NA2 and the second monitoring node NA21, and a third resistor RA3B
is provided between the second monitoring node NA21 and the GND
node. The second capacitor CA2 is provided in the input stage of
the second rectifier circuit 181 (i.e., between the coil end node
NA2 and a high-potential-side resistor end node NA22 between the
second resistor RA2B and the fourth diode DA4B).
The third rectifier circuit 191 outputs the waveform-monitoring
third induced voltage signal PHIN3 to the third waveform detection
circuit 37 through a third monitoring node NA31. Specifically, the
third rectifier circuit 191 includes a fourth resistor RA2C
provided between the coil end node NA2 and the third monitoring
node NA31, and a fifth resistor RA3C provided between the
monitoring node NA31 and the GND node. The third rectifier circuit
191 also includes a fifth diode DA3C provided between the
monitoring node NA31 and the GND node. The voltage of the coil end
signal CSG is divided by the resistors RA2C and RA3C, and the
resulting signal is input to the third waveform detection circuit
37 as the induced voltage signal PHIN3. The diode DA3C subjects the
coil end signal CSG to half-wave rectification so that a negative
voltage is not applied to the third waveform detection circuit
37.
FIG. 12 shows a waveform example of the coil end signal CSG input
to the first rectifier circuit 17 and the second rectifier circuit
181, the induced voltage signal PHIN1 output to the first waveform
detection circuit 31 from the first rectifier circuit 17, the pulse
signal PLS1 used for pulse width detection, the induced voltage
signal PHIN2 output to the second waveform detection circuit 34
from a second rectifier circuit 181, and the pulse signal PLS2 used
for pulse width detection.
As indicated by J1 in FIG. 12, the first waveform detection circuit
31 detects the pulse width period XTPW1 that corresponds to a
change in phase when the induced voltage signal PHIN1 (coil end
signal CSG) rises. Specifically, the first waveform detection
circuit 31 measures the pulse width period XTPW1 that is a period
between the timing at which the induced voltage signal PHIN1 that
has changed from 0 V exceeds the threshold voltage VT1 (see J2) and
the edge timing (the rising edge timing in FIG. 12, but may be the
falling edge timing) of the drive clock signal DRCK. In this case,
since it suffices that a voltage near 0 V be detected, the waveform
need not be reduced. Therefore, voltage division using the
resistors RA2B and RA3B of the rectifier circuit 181 shown in FIG.
11 is unnecessary. This prevents a situation in which the waveform
of the signal PHIN1 is deformed or the signal deteriorates due to a
resistance division node and a parasitic capacitor. Therefore,
since the first waveform detection circuit 31 can detect the
waveform using the signal PHIN1 having a fine waveform, the
detection accuracy can be improved.
When the waveform is not reduced by voltage division using
resistors, the signal PHIN1 may exceed the maximum rated voltage of
the power transmission control device 20. However, since the diode
DA1 is provided in the rectifier circuit 17 and performs the limit
operation that clamps the signal PHIN1 at the voltage VDD (see J3),
a situation in which the signal PHIN1 exceeds the maximum rated
voltage can be prevented. Moreover, since the diode DA2 is provided
in the rectifier circuit 17 and performs half-wave rectification
(see J4), a situation in which a negative voltage is applied to the
IC terminal of the power transmission control device 20 can be
prevented.
As indicated by K1, the second waveform detection circuit 34
detects the pulse width period XTPW2 that corresponds to a change
in phase when the induced voltage signal PHIN2 (coil end signal
CSG) falls. Specifically, the second waveform detection circuit 34
measures the pulse width period XTPW2 that is a period between the
timing at which the induced voltage signal PHIN2 that has changed
from the voltage VDD becomes lower than the threshold voltage VT2
(see K2) and the edge timing (the falling edge timing in FIG. 12,
but may be the rising edge timing) of the drive clock signal DRCK.
Therefore, since it is necessary to reduce the waveform of the coil
end signal CSG that exceeds the voltage VDD, the rectifier circuit
181 performs voltage division using the resistors RA2B and RA3B.
Specifically, the threshold voltage of an N-type transistor can be
used as the threshold voltage VT2 by reducing the waveform of the
coil end signal CSG by dividing the voltage of the coil end signal
CSG, for example. Since the diode DA3B is provided in the rectifier
circuit 181 and performs half-wave rectification (see K3), a
situation in which a negative voltage is applied to the IC terminal
of the power transmission control device 20 can be prevented.
For example, when the induced voltage signal PHIN1 input to the
first waveform detection circuit 31 shown in FIG. 11 is generated
using the rectifier circuit 181 instead of the rectifier circuit
17, the waveform of the induced voltage signal PHIN1 is reduced by
voltage division. Therefore, the waveform is deformed near the
threshold voltage VT1, whereby the detection accuracy may
deteriorate.
In FIG. 11, since the induced voltage signal PHIN1 is generated
using the rectifier circuit 17 that does not perform voltage
division, such a situation can be prevented.
In FIG. 11, circuits (i.e., the rectifier circuits 17 and 181)
having different configurations are used as the circuits that
generate the induced voltage signals PHIN1 and PHIN2 for the first
and second waveform detection circuits 31 and 34, as described
above. The dynamic range and the sensitivity complement each other
by selectively utilizing the rectifier circuits 17 and 181, so
waveform detection (pulse width detection) with high accuracy can
be implemented.
In the fifth configuration example, since the first capacitor CA1
and the second capacitor CA2 are respectively provided in the input
stage of the first rectifier circuit 17 and the second rectifier
circuit 181, the DC offset of the coil end signal CSG can be
canceled by capacitive coupling of the capacitors CA1 and CA2. This
prevents a situation in which a change in DC offset adversely
affects the load state detection accuracy. This enables load state
detection with high sensitivity and a high dynamic range, for
example.
4. First Configuration Example of Power Transmission Device
FIG. 13 shows a first configuration example of the power
transmission device 10. FIG. 13 corresponds to the first
configuration example of the waveform monitoring circuit 14 shown
in FIG. 5.
In FIG. 13, when the inductance of the primary coil L1, the
capacitance of the capacitor that forms the resonant circuit, the
power supply voltage, the distance or the positional relationship
between the primary coil L1 and the secondary coil L2, or the like
has changed, the voltage peak (amplitude) of the induced voltage
signal PHIN1 also changes. Therefore, a change in load may not be
accurate detected by merely detecting the peak voltage of the
induced voltage signal PHIN. In FIG. 13, a change in load is
detected by detecting pulse width information relating to the
induced voltage signal PHIN.
In FIG. 13, the drive clock signal generation circuit 25 generates
the drive clock signal DRCK that specifies the drive frequency of
the primary coil L1. Specifically, the drive clock signal
generation circuit 25 generates the drive clock signal DRCK by
dividing the frequency of a reference clock signal CLK generated by
the oscillation circuit 24. An alternating-current voltage at a
drive frequency specified by the drive clock signal DRCK is
supplied to the primary coil L1.
The driver control circuit 26 generates a driver control signal
based on the drive clock signal DRCK, and outputs the driver
control signal to the power transmission drivers (first and second
power transmission drivers) of the power transmission section 12
that drives the primary coil L1. In this case in order to prevent a
shoot-through current from flowing through the inverter circuit of
the power transmission driver, the driver control circuit 26
generates the driver control signal so that a signal input to the
gate of a P-type transistor of the inverter circuit does not
overlap a signal input to the gate of an N-type transistor of the
inverter circuit.
The waveform detection circuit 30 includes the first waveform
detection circuit 31 that detects a change in waveform of the first
induced voltage signal PHIN1 of the primary coil L1. The first
waveform detection circuit 31 includes the first waveform adjusting
circuit 32 and the first pulse width detection circuit 33. The
waveform adjusting circuit 32 (pulse signal generation circuit)
adjusts the waveform of the induced voltage signal PHIN1 of the
primary coil L1, and outputs a waveform-adjusted signal WFQ1.
Specifically, the waveform adjusting circuit 32 outputs the square
wave (rectangular wave) waveform-adjusted signal WFQ1 (pulse
signal) that becomes active (e.g., H level) when the signal PHIN1
has exceeded a given threshold voltage, for example.
The pulse width detection circuit 33 detects pulse width
information relating to the induced voltage signal PHIN1 of the
primary coil L1. Specifically, the pulse width detection circuit 33
receives the waveform-adjusted signal WFQ1 from the waveform
adjusting circuit 32 and the drive clock signal DRCK (drive control
signal) from the drive clock signal generation circuit 25, and
detects the pulse width information relating to the
waveform-adjusted signal WFQ1 to detect the pulse width information
relating to the induced voltage signal PHIN1.
For example, a timing at which the induced voltage signal PHIN1
that has changed from the voltage GND (low-potential-side power
supply voltage) exceeds the first threshold voltage VT1 is referred
to as a first timing. In this case, the pulse width detection
circuit 33 measures a first pulse width period that is a period
between a first edge timing (e.g., falling edge timing) of the
drive clock signal DRCK and the first timing to detect first pulse
width information. For example, the pulse width detection circuit
33 measures the first pulse width period in which the voltage
signal PHIN1 induced by a change in voltage of the drive clock
signal DRCK becomes equal to or lower than the given threshold
voltage VT1. The pulse width detection circuit 33 measures the
pulse width of the waveform-adjusted signal WFQ1 (induced voltage
signal) with respect to the pulse width of the drive clock signal
DRCK. In this case, the first pulse width period is measured using
the reference clock signal CLK, for example. A latch circuit (not
shown) latches measurement result data PWQ1 obtained by the pulse
width detection circuit 33 for example. Specifically, the pulse
width detection circuit 33 measures the first pulse width period
using a counter that increments (or decrements) the count value
based on the reference clock signal CLK, and the latch circuit
latches the measurement result data PWQ1.
The control circuit 22 detects the power-reception-side
(secondary-side) load state (change in load or degree of load)
based on the pulse width information detected by the pulse width
detection circuit 33. Specifically, the control circuit 22 performs
foreign object detection (primary foreign object detection) based
on the pulse width information detected by the pulse width
detection circuit 33. The control circuit 22 may detect data
transmitted from the power reception device 40 by means of load
modulation.
FIGS. 14A to 14C show measurement results for the signal waveforms
of the drive clock signal DRCK, the coil end signal CSG, the
induced voltage signal PHIN1, and the pulse signal PLS1. FIGS. 14A,
14B, and 14C show signal waveforms (voltage waveforms) in a
low-load state (e.g., secondary-side load current=0 mA), a
medium-load state (load current=70 mA), and a high-load state (load
current=150 mA), respectively. The pulse signal PLS1 used for pulse
width detection is a signal that is set at the H level at a first
timing TM1 at which the induced voltage signal PHIN1 exceeds the
first threshold voltage VT1 and is set at the L level at a rising
edge timing TR of the drive clock signal DRCK. As the threshold
voltage VT1 (e.g. a threshold voltage of an N-type transistor) used
to measure the pulse width period, a voltage at which the load
state detection accuracy is optimized may be appropriately
selected.
As shown in FIGS. 14A to 14C, the pulse width period XTPW1 of the
pulse signal PLS1 increases as the power-reception-side load
increases (i.e., the load current increases). Therefore, the
power-reception-side load state (degree of load) can be detected by
measuring the pulse width period XTPW1. For example, when a foreign
object such as a metal foreign object has been placed on the
primary coil L1 (inserted between the primary coil L1 and the
secondary coil L2), power is supplied to the foreign object from
the primary-side instrument, whereby the power-reception-side
instrument is overloaded. In this case, the overload state can be
detected by measuring the pulse width period XTPW1 so that foreign
object detection (primary foreign object detection) can be
implemented. Moreover, whether the data transmitted from the
power-reception-side instrument is "0" or "1" can be detected by
determining the degree of load of the load modulation section 46 of
the power reception device 40 by measuring the pulse width period
XTPW1.
In FIGS. 14A to 14C, the period from the timing TM1 to the rising
edge timing TR of the drive clock signal DRCK is defined as the
pulse width period XTPW1. In this case, the first waveform
detection circuit 31 detects the pulse width period XTPW1 of the
pulse signal PLS1 as the first pulse width information. Note that
it is desirable that the period from a falling edge timing TF of
the drive clock signal DRCK to the timing TM1 be specified as a
pulse width period TPW1 (see FIG. 17), and the first waveform
detection circuit 31 detect the pulse width period TPW1 as the
first pulse width information. This prevents a situation in which
the pulse width period is measured while regarding a noise signal
as a pulse signal when the power-reception-side load is low. In
this case, the pulse width period TPW1 decreases as the
power-reception-side load increases. This makes it possible to
determine that a foreign object has been placed (inserted) on the
primary coil L1 when the pulse width period TPW1 (pulse width
count) has become shorter than a given period (Given count),
whereby foreign object detection can be implemented.
FIG. 15A shows a primary-side equivalent circuit in a no-load
state, and FIG. 15B shows a primary-side equivalent circuit in a
load-connected state. As shown in FIG. 15A, a series resonant
circuit is formed by a capacitance C, a primary-side leakage
inductance L11, and a coupling inductance M. Therefore, the
resonance characteristics in a no-load state have a sharp profile
with a high Q value, as indicated by B1 in FIG. 15C. A
secondary-side leakage inductance L12 and a resistance RL of the
secondary-side load are added in a load-connected state. Therefore,
resonance frequencies fr2 and fr3 in a load-connected state are
higher than a resonance frequency fr1 in a no-load state, as shown
in FIG. 15C. The resonance characteristics in a load-connected
state have a gentle profile with a low Q value due to the effect of
the resistance RL. The resonance frequency increases as the load
increases from a low-load state (RL: high) to a high-load state
(RL: low), and approaches the drive frequency of the coil
(frequency of the drive clock signal DRCK).
When the resonance frequency approaches the drive frequency, a sine
wave (resonance waveform) is gradually observed. In the voltage
waveform in a low-load state shown in FIG. 14A, a square wave
(drive waveform) is predominant over a sine wave (resonance
waveform). In the voltage waveform in a high-load state shown in
FIG. C1, a sine wave (resonance waveform) is predominant over a
square wave (drive waveform). As a result, the pulse width period
XTPW1 increases (the pulse width period TPW1 decreases) as the load
increases. Therefore, a change (degree) in power-reception-side
load can be determined using a simple configuration by measuring
the pulse width period XTPW1 (TPW1).
For example, a change in power-reception-side load due to insertion
of a metal foreign object or the like may be determined by
detecting only a change in peak voltage of the coil end signal.
However, the peak voltage also changes due to the distance or the
positional relationship between the primary coil L1 and the
secondary coil L2 in addition to a chance in load. Therefore, a
variation in load change detection increases.
In the pulse width detection method according to this embodiment, a
chance in load is detected by measuring the pulse width period that
changes due to the power-reception-side load state by digital
processing instead of detecting the peak voltage. Therefore, a
change in load can be detected with a small variation.
A change in power-reception-side load may be determined based on
phase characteristics due to load. The term "phase characteristics
due to load" used herein refers to a voltage/current phase
difference. This method complicates the circuit configuration and
increases cost.
In the pulse width detection method according to this embodiment,
since digital data can be processed using a simple waveform
adjusting circuit and a counter circuit (counter) utilizing the
voltage waveform, the circuit configuration can be simplified.
Moreover, the pulse width detection method according to this
embodiment can be easily combined with the amplitude detection
method that detects a change in load by detecting the peak
voltage.
In the pulse width detection method according to this embodiment,
the pulse width period XTPW1 specified by the timing TM1 at which
the induced voltage signal PHIN1 that has changed from 0 V (GND)
exceeds the threshold voltage VT1 is measured, as shown in FIGS.
14A to 14C. Therefore, an adverse effect due to a change in power
supply voltage or a change in distance or positional relationship
between the primary coil and the secondary coil can be reduced by
setting the threshold voltage VT1 at a value close to 0 V, whereby
a change in load can be detected with a further reduced
variation.
FIG. 16 shows a specific example of the first configuration example
of the power transmission device 10 according to this
embodiment.
The waveform adjusting circuit 32 includes a resistor RC1 and an
N-type transistor TC1 connected in series between the power supply
VDD (high-potential-side power supply) and the power supply GND
(low-potential-side power supply), and an inverter circuit INVC.
The induced voltage signal PHIN1 from the waveform monitoring
circuit 14 is input to the gate of the transistor TC1. When the
signal PHIN1 has exceeded the threshold voltage of the transistor
TC1, the transistor TC1 is turned ON so that the voltage of a node
NC1 is set at the L level. Therefore, the waveform-adjusted signal
WFQ1 is set at the H level. When the signal PHIN1 has become lower
than the threshold voltage, the waveform-adjusted signal WFQ1 is
set at the L level.
The pulse width detection circuit 33 includes a first counter 122.
The counter 122 increments (or decrements) the count value in the
pulse width period, and measures the pulse width period (first
pulse width period) based on the resulting count value. In this
case, the counter 122 counts the count value based on the reference
clock signal CLK, for example.
More specifically, the pulse width detection circuit 33 includes a
first enable signal generation circuit 120. The enable signal
generation circuit 120 receives the first waveform-adjusted signal
WFQ1 and the drive clock signal DRCK, and generates a first enable
signal ENQ1 that becomes active in the first pulse width period.
The counter 122 increments (or decrements) the count value when the
enable signal ENQ1 is active (e.g., H level).
The enable signal generation circuit 120 may be formed using a
flip-flop circuit FFC1, the drive clock signal DRCK (including a
signal equivalent to the drive clock signal DRCK) being input to a
clock terminal (inverting clock terminal) of the flip-flop circuit
FFC1, a voltage VDD (high-potential-side power supply voltage)
being input to a data terminal of the flip-flop circuit FFC1, and
the waveform-adjusted signal WFQ1 (including a signal equivalent to
the waveform-adjusted signal WFQ1) being input to a reset terminal
(non-inverting reset terminal) of the flip-flop circuit FFC1. When
the waveform-adjusted signal WFQ1 is set at the L level and the
drive clock signal DRCK is then set at the L level, the enable
signal ENQ1 (i.e., output signal) from the flip-flop circuit FFC1
is set at the H level (active). When the waveform-adjusted signal
WFQ1 is set at the H level, the flip-flop circuit FFC1 is reset so
that the enable signal ENQ1 (output signal) from the flip-flop
circuit FFC1 is set at the L level (inactive). Therefore, the
counter 122 can measure the pulse width period by counting the
period in which the enable signal ENQ1 is set at the H level
(active) based on the reference clock signal CLK.
Note that the enable signal generation circuit 120 may be formed
using a flip-flop circuit, the drive clock signal DRCK being input
to a clock terminal of the flip-flop circuit, a data terminal of
the flip-flop circuit being connected to the power supply GND
(low-potential-side power supply), and the waveform-adjusted signal
WFQ1 being input to a set terminal of the flip-flop circuit. In
this case, a signal obtained by inverting the output signal from
the flip-flop circuit may be input to the counter 122 as the enable
signal ENQ1.
A count value holding circuit 124 holds a count value CNT1 (pulse
width information) from the counter 122. The count value holding
circuit 124 outputs data LTQ1 relating to the held count value to
an output circuit 126.
The output circuit 126 (filter circuit or noise removal circuit)
receives the data LTQ1 relating to the count value held by the
count value holding circuit 124, and outputs the data PWQ1 (first
pulse width information). The output circuit 126 may include a
comparison circuit 130 that compares the count value currently held
by the count value holding circuit 124 with the count value
previously held by the count value holding circuit 124, and outputs
the count value larger than the other, for example. This allows the
maximum count value to be held by and output from the output
circuit 126. This suppresses a change in pulse width period due to
noise or the like, whereby the pulse width can be stably detected.
Moreover, the pulse width detection method can be easily combined
with the amplitude detection method.
FIG. 17 shows a signal waveform example illustrative of the
operation of the circuit shown in FIG. 16. When the
waveform-adjusted signal WFQ1 is set at the L level at a timing
indicated by D1 in FIG. 17, the reset state of the flip-flop
circuit FFC1 is canceled. The voltage VDD is input to the flip-flop
circuit FFC1 at the falling edge timing TF of the drive clock
signal DRCK, whereby the enable signal ENQ1 changes from the L
level to the H level. This causes the counter 122 to start the
count process and measure the pulse width period TPW1 using the
reference clock signal CLK.
When the waveform-adjusted signal WFQ1 is set at the H level at the
first timing TM1, the flip-flop circuit FFC1 is reset so that the
enable signal ENQ1 changes from the H level to the L level. This
causes the counter 122 to stop the count process. The count value
obtained by the count process is the measurement result that
indicates the pulse width period TPW1.
As shown in FIG. 17, the sum of the pulse width periods TPW1 and
XTPW1 corresponds to the half-cycle period of the drive clock
signal DRCK. The pulse width period XTPW1 shown in FIGS. 14A to 14C
increases as the power-reception-side load increases. Therefore,
the pulse width period TPW1 shown in FIG. 17 decreases as the
power-reception-side load increases. In the pulse width period
XTPW1 shown in FIGS. 14A to 14C, it is difficult to distinguish a
noise signal from a pulse signal when the power-reception-side load
is low. Such a problem can be prevented using the pulse width
period TPW1 shown in FIG. 17.
In the first pulse width detection method according to this
embodiment, the pulse width period TPW1 is specified based on the
timing TM1 at which the coil end signal CSG that has changed from 0
V exceeds a low-potential-side threshold voltage VTL, as indicated
by D3 in FIG. 17. Specifically, the pulse width period TPW1 is the
period between the falling edge timing TF of the drive clock signal
CLK and the timing TM1. The pulse width period TPW1 changes when
the timing TM1 has changed due to a change in power-reception-side
change in load. Since the threshold voltage VTL that determines the
timing TM1 is low, the timing TM1 varies to only a small extent
even if the power supply voltage or the like has changed. The
timing TM1 varies to only a small extent even if the distance or
the positional relationship between the coils L1 and L2 has
changed. Therefore, the first method according to this embodiment
implements a pulse width detection method that reduces an adverse
effect of a change in power supply voltage or the like.
The rectifier circuit 17 shown in FIG. 16 outputs the coil end
signal CSG to the waveform adjusting circuit 32 as the induced
voltage signal PHIN1 without dividing the voltage of the coil end
signal CSG, differing from the rectifier circuit 18 (see FIG. 22)
described later utilizing the second method according to this
embodiment. Therefore, the threshold voltage VTL shown in FIG. 17
is almost equal to the threshold voltage of the N-type transistor
TC1 of the waveform adjusting circuit 32 shown in FIG. 16, and is
almost equal to the threshold voltage VT1 shown in FIGS. 14A to
14C.
Note that the configuration of the waveform adjusting circuit 32 is
not limited to the configuration shown in FIG. 16. For example, the
waveform adjusting circuit 32 may be formed using a comparator or
the like. The configuration of the enable signal generation circuit
120 is not limited to the configuration shown in FIG. 16. For
example, the enable signal generation circuit 120 may be formed
using a logic circuit such as a NOR circuit or a NAND circuit. The
configuration of the output circuit 126 is not limited to the
configuration shown in FIG. 16. For example, the output circuit 126
may be formed using an averaging circuit that calculates the
average value (moving average) of a plurality of count values
(e.g., the current count value and the preceding count value).
5. Second Configuration Example of Power Transmission Device
FIG. 18 shows a second configuration example of the power
transmission device 10. FIG. 18 corresponds to the fourth
configuration example of the waveform monitoring circuit 14 shown
in FIG. 8. The power transmission device 10 may be configured so
that the waveform monitoring circuit 14 of the power transmission
device shown in FIG. 18 corresponds to the fifth configuration
example shown in FIG. 11.
In FIG. 18, the waveform detection circuit 30 includes the second
waveform detection circuit 34 that detects a change in waveform of
the second induced voltage signal PHIN2 of the primary coil L1 in
addition to the first waveform detection circuit 31 described with
reference to FIGS. 13 and 16. The first waveform detection circuit
31 detects the pulse width using the first pulse width detection
method described with reference to FIGS. 14A to 14C and the like.
On the other hand, the second waveform detection circuit 34 detects
the pulse width using the second pulse width detection method
described later with reference to FIGS. 19A to 19C.
The second waveform detection circuit 34 includes a second waveform
adjusting circuit 35 and a second pulse width detection circuit 36.
The waveform adjusting circuit 35 adjusts the waveform of the
induced voltage signal PHIN2 of the primary coil L1, and outputs a
waveform-adjusted signal WFQ2. Specifically, the waveform adjusting
circuit 35 outputs the square wave (rectangular wave)
waveform-adjusted signal WFQ1 that becomes active (e.g., H level)
when the signal PHIN2 has exceeded a given threshold voltage, for
example.
The pulse width detection circuit 36 detects pulse width
information relating to the induced voltage signal PHIN2 of the
primary coil L1. Specifically, the pulse width detection circuit 36
receives the waveform-adjusted signal WFQ2 from the waveform
adjusting circuit 35 and the drive clock signal DRCK from the drive
clock signal generation circuit 25, and detects the pulse width
information relating to the waveform-adjusted signal WFQ2 to detect
the pulse width information relating to the induced voltage signal
PHIN2.
For example, a timing at which the induced voltage signal PHIN2
that has changed from the high-potential-side power supply voltage
(VDD) has become lower than the second threshold voltage VT2 is
referred to as a second timing. In this case, the pulse width
detection circuit 36 measures a second pulse width period that is a
period between a second edge timing (e.g., rising edge timing) of
the drive clock signal DRCK and the second timing to detect second
pulse width information. For example, the pulse width detection
circuit 36 measures the second pulse width period in which the
voltage signal PHIN2 induced by a change in voltage of the drive
clock signal DRCK becomes equal to or higher than the given
threshold voltage VT2. The pulse width detection circuit 36
measures the pulse width of the waveform-adjusted signal WFQ2
(induced voltage signal) with respect to the pulse width of the
drive clock signal DRCK. In this case, the pulse width detection
circuit 36 measures the pulse width period using the reference
clock signal CLK, for example. A latch circuit (not shown) latches
measurement result data PWQ2 obtained by the pulse width detection
circuit 36, for example. Specifically, the pulse width detection
circuit 36 measures the pulse width period using a counter that
increments (or decrements) the count value based on the reference
clock signal CLK, and the latch circuit latches the measurement
result data PWQ2.
The control circuit 22 performs foreign object detection (secondary
foreign object detection) based on the pulse width information
detected by the pulse width detection circuit 36. Alternatively,
the control circuit 22 detects data transmitted from the power
reception device 40 by means of load modulation.
FIGS. 19A to 19C show measurement results for the signal waveforms
of the drive clock signal DRCK, the coil end signal CSG, the
induced voltage signal PHIN2, and the pulse signal PLS2. FIGS. 19A,
19B, and 19C show signal waveforms in a low-load state, a
medium-load state, and a high-load state, respectively. The pulse
signal PLS2 used for pulse width detection is a signal that is set
at the H level at a second timing TM2 at which the induced voltage
signal PHIN2 becomes lower than the second threshold voltage VT2,
and is set at the L level at a falling edge timing TF of the drive
clock signal DRCK. As the threshold voltage VT2 (e.g., a threshold
voltage of an N-type transistor) used to measure the pulse width
period, a voltage at which the load state detection accuracy is
optimized may be appropriately selected.
As shown in FIGS. 19A to 19C, the pulse width period XTPW2 of the
pulse signal PLS2 increases as the power-reception-side load
increases. Therefore, the power-reception-side load state can be
detected by measuring the pulse width period XTPW2. Specifically, a
foreign object can be detected (secondary foreign object
detection), or whether data (save frame) transmitted from the
power-reception-side instrument is "0" or "1" can be detected.
In FIGS. 19A to 19C, the period from the timing TM2 to the falling
edge timing TF of the drive clock signal DRCK is defined as the
pulse width period XTPW2. In this case, the second waveform
detection circuit 34 detects the pulse width period XTPW2 of the
pulse signal PLS2 as the second pulse width information. Note that
it is desirable that the period from a rising edge timing TR of the
drive clock signal DRCK to the timing TM2 be specified as the pulse
width period TPW2 (see FIG. 23), and the second waveform detection
circuit 33 detect the pulse width period TPW2 as the second pulse
width information. This prevents a situation in which the pulse
width period is measured while regarding a noise signal as a pulse
signal when the power-reception-side load is low. In this case, the
pulse width period TPW2 decreases as the power-reception-side load
increases.
The second method (falling edge detection system) shown in FIGS.
19A to 19C has an advantage over the first method (rising edge
detection method) shown in FIGS. 14A to 14C in that the pulse width
(count value) changes to a large extent even if a change in load is
small so that high sensitivity is achieved. On the other hand, the
first method shown in FIGS. 14A to 14C has an advantage over the
second method shown in FIGS. 19A to 19C in that a variation in
pulse width detection is small with respect to a change in power
supply voltage or a change in distance or positional relationship
between the coils L1 and L2.
FIG. 20A is a view showing a variation in pulse width detection
with respect to a change in power supply voltage when using the
first method, and FIG. 20B is a view showing a variation in pulse
width detection with respect to a change in power supply voltage
when using the second method.
As shown in FIG. 20A, the load current-pulse width characteristic
curve does not change to a large extent when using the first method
even if the power supply voltage has increased or decreased. As
shown in FIG. 20B, when using the second method, the load
current-pulse width characteristic curve changes when the power
supply voltage has increased or decreased (i.e., a variation in
pulse width detection with respect to a change in power supply
voltage is large).
In the second configuration shown in FIG. 18, the first waveform
detection circuit 31 detects the waveform using the first method
and the resulting first pulse width information (PWQ1) is used
during primary foreign object detection (i.e., foreign object
detection before normal power transmission starts). The second
waveform detection circuit 34 detects the waveform using the second
method and the resulting second pulse width information (PWQ2) is
used during secondary foreign object detection (i.e., foreign
object detection after normal power transmission has started). Data
(data that indicates full-charge detection or the like) transmitted
from the power-reception-side instrument is also detected using the
second pulse width information, for example.
FIG. 21 is a flowchart illustrative of primary foreign object
detection and secondary foreign object detection.
The primary-side instrument (power transmission device) is
activated (step S21). The activated primary-side instrument
transmits power (power for position detection) for activating the
secondary-side instrument (step S22), and transitions to a
communication standby state (step S23). The secondary-side
instrument (power reception device) is then activated (step S31),
and transmits an authentication frame (synchronization ID) to the
primary-side instrument by means of load modulation described with
reference to FIG. 3B (step S32).
When the primary-side instrument has received the authentication
frame, the primary-side instrument performs ID authentication (step
S24). The primary-side instrument then sets the drive frequency
(frequency of the drive clock signal DRCK) at a foreign object
detection frequency F2 differing from a normal power transmission
frequency F1. Specifically, the primary-side instrument then sets
the drive frequency at the foreign object detection frequency F2
that is a frequency between the normal power transmission frequency
F1 and a coil resonance frequency F0.
The primary-side instrument performs primary foreign object
detection in a state in which the drive frequency is set at the
foreign object detection frequency F2 (step S26). Specifically, the
primary-side instrument performs primary foreign object detection
by causing the first waveform detection circuit 31 to detect the
waveform using the first method described with reference to FIGS.
14A to 14C.
The primary-side instrument then sets the drive frequency at the
normal power transmission frequency F1, and starts normal power
transmission (step S27). The secondary-side instrument receives
power transmitted from the primary-side instrument (step S33).
After normal power transmission has stared, the secondary-side
instrument performs secondary foreign object detection (step S28).
Specifically, the primary-side instrument performs secondary
foreign object detection by causing the second waveform detection
circuit 34 to detect the waveform using the second method described
with reference to FIGS. 19A to 19C. In this case, it is desirable
that the secondary-side instrument regularly perform secondary
foreign object detection after normal power transmission has
started.
When the secondary-side instrument has detected that the load has
been fully charged, the secondary-side instrument requests the
primary-side instrument to stop normal power transmission (step
S34). The primary-side instrument then stops normal power
transmission (step S29).
In FIG. 21, primary foreign object detection is performed in a
no-load state before normal power transmission starts, for example.
Primary foreign object detection is performed using the first
method that reduces a variation with respect to a change in power
supply voltage or the like (see FIG. 20A). Therefore, a foreign
object can be stably detected even if a change in power supply
voltage or the like has occurred. Moreover, the pulse width count
value obtained by primary foreign object detection can be set as a
reference value. Secondary foreign object detection after normal
power transmission can be performed, or whether data transmitted
from the power-reception-side instrument is "0" or "1" can be
detected, based on the reference value in a no-load state, whereby
a change in load can be efficiently detected.
FIG. 22 shows a specific example of the second configuration
example of the power transmission device 10 according to this
embodiment. In FIG. 22, the waveform adjusting circuit 35 of the
second waveform detection circuit 34 has a configuration similar to
that of the waveform adjusting circuit 32 of the first waveform
detection circuit 31. An enable signal generation circuit 140 of
the second waveform detection circuit 34 is configured so that the
drive clock signal DRCK is input to a non-inverting clock terminal
of a flip-flop circuit FFC2, and the waveform-adjusted signal WFQ2
is input to an inverting reset terminal of the flip-flop circuit
FFC2. The configurations of a counter 142, a count value holding
circuit 144, and an output circuit 146 of the second waveform
detection circuit 34 are the same as the configurations of the
counter 122, the count value holding circuit 124, and the output
circuit 126 of the first waveform detection circuit 31.
FIG. 23 shows a signal waveform example illustrative of the
operation of the circuit shown in FIG. 22. When the
waveform-adjusted signal WFQ2 is set at the H level at a timing
indicated by D2 in FIG. 23, the reset state of the flip-flop
circuit FFC2 is canceled. The voltage VDD is input to the flip-flop
circuit FFC2 at the rising edge timing TR of the drive clock signal
DRCK, whereby the enable signal ENQ2 changes from the L level to
the H level. This causes the counter 142 to start the count process
and measure the pulse width period TPW2 using the reference clock
signal CLK.
When the waveform-adjusted signal WFQ2 is set at the L level at the
second timing TM2, the flip-flop circuit FFC2 is reset so that the
enable signal ENQ2 changes from the L1 level to the L level. This
causes the counter 142 to stop the count process. The count value
obtained by the count process is the measurement result that
indicates the pulse width period TPW2.
As shown in FIG. 23, the sum of the pulse width periods TPW2 and
XTPW2 corresponds to the half-cycle period of the drive clock
signal DRCK. The pulse width period XTPW2 shown in FIGS. 19A to 19C
increases as the power-reception-side load increases. Therefore,
the pulse width period TPW2 shown in FIG. 23 decreases as the
power-reception-side load increases. In the pulse width period
XTPW2 shown in FIGS. 19A to 19C, it is difficult to distinguish a
noise signal from a pulse signal when the power-reception-side load
is low. Such a problem can be prevented using the pulse width
period TPW2 shown in FIG. 23.
The timing TM1 is determined using a low-potential-side threshold
voltage VTL (see D3 in FIG. 23) when using the first method, and
the timing TM2 is determined using a high-potential-side threshold
voltage VTH (see D4) when using the second method.
When the rectifier circuit 18 for the second method (see FIG. 22)
is used when using the first method that determines the timing TM1
using the low-potential-side threshold voltage VTL (see D3 in FIG.
23), the waveform may be deformed due to voltage division using the
resistors RA2 and RA3, whereby the detection accuracy may
deteriorate.
The rectifier circuit 17 used for the first method shown in FIG. 22
can input the signal PHIN1 obtained by subjecting the coil end
signal CSG to the clamp operation and half-wave rectification to
the first waveform monitoring circuit 31 without performing voltage
division using a resistor. Therefore, the pulse width can be
detected based on the signal PHIN1 that has a fine waveform (i.e.,
is not subjected to voltage division using a resistor). As a
result, the detection accuracy can be improved. Moreover, a
situation in which the signal PHIN1 exceeds the maximum rated
voltage or a negative voltage is input to the first waveform
detection circuit 31 can be prevented by providing the diodes DA1
and DA2.
On the other hand, the rectifier circuit 18 used for the second
method outputs the signal PHIN2 of which the voltage has been
divided by the resistors RA2 and RA3 to an N-type transistor TC2 of
the waveform adjusting circuit 35. A situation in which the signal
PHIN2 exceeds the maximum rated voltage can be prevented by
dividing the voltage of the signal PHIN2. Moreover, the
high-potential-side threshold voltage VTH can be set, as indicated
by D4 in FIG. 23. Specifically, the signals PHIN1 and PHIN2 are
respectively input to the gates of the N-type transistors TC1 and
TC2 having the same threshold voltage. However, since the signal
PHIN2 is obtained by voltage division using the resistors RA2 and
RA3, the threshold voltage VTH indicated by D4 is higher than the
threshold voltage VTL indicated by D3 with respect to the coil end
signal CSG. A chance in pulse width with respect to a change in
load increases by setting the threshold voltage VTH at such a high
voltage, whereby a change in load can be detected with high
sensitivity. Therefore, secondary foreign object detection after
normal power transmission has started or determination of whether
data transmitted from the secondary-side instrument is "1" or "0"
can be appropriately performed.
In FIG. 22, the first rectifier circuit 17 for the first pulse
width detection method and the second rectifier circuit 18 for the
second pulse width detection method are provided. Note that a third
rectifier circuit for peak detection (voltage detection) may also
be provided. A third waveform detection circuit that receives a
third induced voltage signal from the third rectifier circuit for
peak detection may be provided in addition to the first waveform
detection circuit and the second waveform detection circuit. In
this case, the third waveform detection circuit detects a change in
power-reception-side load by detecting a change in the peak of the
third induced voltage signal. The third waveform detection circuit
may include an amplitude detection circuit that performs a
peak-hold operation, and an A/D conversion circuit that subjects a
signal of which the peak has been held by the amplitude detection
circuit to A/D conversion, and the like. More intelligent waveform
detection can be implemented by providing the third rectifier
circuit and the third waveform detection circuit for amplitude
detection to combine peak detection and pulse width detection.
FIG. 24 shows a specific configuration example of the third
waveform detection circuit 37 included in the waveform detection
circuit 30 according to the fifth configuration example shown in
FIG. 11.
As shown in FIG. 24, the third waveform detection circuit 37
includes an amplitude detection circuit 331, an A/D conversion
circuit 332, and a latch circuit 333. The amplitude detection
circuit 331 includes operational amplifiers OPA1 and OPA2, a hold
capacitor CA3, and a reset N-type transistor TA1. A signal PHIN3 is
input to a non-inverting input terminal of the operational
amplifier OPA1, and an output node NA5 of the operational amplifier
OPA2 is connected to an inverting input terminal of the operational
amplifier OPA1. The hold capacitor CA3 and the reset transistor TA1
are provided between a peak voltage hold node NA4 (i.e., output
node of the operational amplifier OPA1) and the power supply GND
(low-potential-side power supply). The hold node NA4 is connected
to a non-inverting input terminal of the operational amplifier
OPA2, and the output node NA5 of the operational amplifier OPA2 is
connected to an inverting input terminal of the operational
amplifier OPA2 so that the operational amplifier OPA2 forms a
voltage-follower-connected operational amplifier. A
voltage-follower-connected operational amplifier may be further
provided in the subsequent stage of the operational amplifier
OPA2.
The operational amplifiers OPA1 and OPA2, the hold capacitor CA3,
and the reset transistor TA1 shown in FIG. 24 form a peak-hold
circuit (peak detection circuit). Specifically, the peak voltage of
the signal PHIN3 from the third rectifier circuit 191 of the
waveform monitoring circuit 14 is held by the hold node NA4, and
the peak voltage signal held by the hold node NA4 is subjected to
impedance conversion by the voltage-follower-connected operational
amplifier OPA2 and is output to the node NA5.
The reset transistor TA1 is turned ON in a reset period to
discharge the hold node NA4 toward the power supply GND.
Specifically, the operational amplifier OPA1 is an operational
amplifier that merely stores a charge in the hold capacitor CA3,
but cannot discharge a charge toward the power supply GND.
Therefore, the operational amplifier OPA1 can follow an increase in
the peak voltage of the signal PHIN3, but cannot follow a decrease
in the peak voltage of the signal PHIN3. A leakage current exists
in a charge-storage P-type transistor provided in an output section
of the operational amplifier OPA1. Therefore, even if the P-type
transistor is turned OFF, the voltage of the hold node NA4
increases with the passage of time. Accordingly, it is necessary to
regularly reset the voltage of the hold node NA4. In FIG. 24, the
reset transistor TA1 is provided for the hold node NA4 for the
above reasons.
In this embodiment, the power-reception-side instrument detects
(extracts) a clock signal from the power-transmission-side
alternating-current voltage, and performs load modulation in
synchronization with the clock signal, for example. Therefore,
since the power-reception-side instrument performs load modulation
in synchronization with the power-transmission-side clock signal,
the power-transmission-side instrument can uniquely determine the
power-reception-side load modulation timing. Therefore, the control
circuit 22 specifies the load switch timing of the
power-reception-side load modulation, and performs reset control
which discharges the hold node NA4 toward the power supply GND in a
reset period including the specified switch timing. This implements
an appropriate peak-hold operation even when employing the
operational amplifier OPA1 that cannot follow a decrease in peak
voltage. Moreover, an increase in the held voltage due to a leakage
current of the P-type transistor of the operational amplifier OPA1
can be prevented by regularly resetting the voltage of the hold
node NA4 in a standby mode when waiting for the peak voltage to
exceed a provisional voltage SIGH0.
FIG. 25 shows a signal waveform example illustrative of the
operation of the amplitude detection circuit 331. As shown in FIG.
25, the signal PHIN3 is a signal that is half-wave rectified by the
third rectifier circuit 191 that is a half-wave rectifier circuit.
The voltage of an output signal OPQ from the operational amplifier
OPA1 increases in a pulse generation period of the signal PHIN3.
The voltage of the output signal OPQ is held by the hold capacitor
CA3 and is maintained in a pulse non-generation period. An output
signal PHQ from the operational amplifier OPA2 smoothly follows the
peak of the signal PHIN.
The A/D conversion circuit 332 includes a sample/hold circuit 334,
a comparator CPA1, a successive approximation register 336, and a
D/A conversion circuit 335. The sample/hold circuit 334 samples and
holds the signal PHQ. The comparator CPA1 compares a D/A-converted
analog signal DAQ from the D/A conversion circuit 335 with a
sample/hold signal SHQ from the sample/hold circuit 334. The
successive approximation register 336 (successive approximation
type control circuit) stores data relating to an output signal CQ1
from the comparator CPA1. The D/A conversion circuit 335 subjects
digital data SAQ (e.g., eight bits) from the successive
approximation register 336 to D/A conversion, and outputs the
analog signal DAQ.
In the successive approximation A/D conversion circuit 332, the
comparator CPA1 compares the D/A-converted signal DAQ when only the
most significant bit (MSB) is set at "1" with the input signal SHQ
(PHQ). When the voltage of the signal SHQ is higher than the
voltage of the signal DAQ, the comparator CPA1 maintains the MSB at
"1". When the voltage of the signal SHQ is lower than the voltage
of the signal DAQ, the comparator CPA1 sets the MSB at "0". The A/D
conversion circuit 332 performs the successive approximation
process on the lower-order bits in the same manner as described
above. The A/D conversion circuit 208 outputs the resulting digital
data ADQ to the latch circuit 333. Note that the A/D conversion
circuit 332 is not limited to the configuration shown in FIG. 24.
For example, the A/D conversion circuit 29 may be a successive
approximation type A/D conversion circuit having a different
circuit configuration, or may be a servo-balancing type, parallel
comparison type, or dual-slope type A/D conversion circuit.
For example, removal detection (detachment detection) that detects
that the portable telephone 510 shown in FIG. 1A has been removed
from the charger 500 can be implemented by using the third waveform
detection circuit 37 having the configuration shown in FIG. 24.
Specifically, when the portable telephone 510 has been removed from
the charger 500, the amplitude of the coil end signal CSG changes,
as is clear from FIG. 3B. In FIG. 24, the amplitude detection
circuit 331 detects the amplitude (peak voltage) of the coil end
signal CSG, and the A/D conversion circuit 332 converts the
detected amplitude into a digital value. The control circuit 22
compares the digital value corresponding to the amplitude (peak
voltage) obtained and a digital value corresponding to a threshold
voltage to detect a change in the amplitude of the coil end signal
CSG shown in FIG. 3B, thereby detecting that the portable telephone
510 has been removed from the charger 500.
The first waveform detection circuit 31 shown in FIG. 11 performs
primary foreign object detection (step S26 in FIG. 21) before
normal power transmission starts using the first waveform detection
method (rising edge detection method).
The second waveform detection circuit 34 shown in FIG. 11 performs
secondary foreign object detection (step S28 in FIG. 21) after
normal power transmission has started, or detects data transmitted
from the power-reception-side instrument using the second waveform
detection method (falling edge detection method).
In FIG. 11, the first waveform detection circuit 31 performs
primary foreign object detection, the second waveform detection
circuit 34 performs secondary foreign object detection or data
detection, and the third waveform detection circuit 37 performs
removal detection, as described above. More intelligent waveform
detection can be implemented by selectively utilizing the waveform
detection circuits.
Although some embodiments of the invention have been described in
detail above, those skilled in the art would readily appreciate
that many modifications are possible in the embodiments without
materially departing from the novel teachings and advantages of the
invention. Accordingly, such modifications are intended to be
included within the scope of the invention. Any term (e.g., GND,
VDD, and portable telephone/charger) cited with a different term
(e.g. low-potential-side power supply, high-potential-side power
supply, and electronic instrument) having a broader meaning or the
same meaning at least once in the specification and the drawings
can be replaced by the different term in any place in the
specification and the drawings. The invention also includes any
combinations of the embodiments and the modifications. The
configurations and the operations of the power transmission control
device, the power transmission device, the power reception control
device, and the power reception device, and the pulse width
detection method are not limited to those described relating to the
above embodiments. Various modifications and variations may be
made.
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